[PATCH v5 00/20] job: replace AioContext lock with job_mutex

[PATCH v5 00/20] job: replace AioContext lock with job_mutex

[Emanuele Giuseppe Esposito]

In this series, we want to remove the AioContext lock and instead
use the already existent job_mutex to protect the job structures
and list. This is part of the work to get rid of AioContext lock
usage in favour of smaller granularity locks.

In order to simplify reviewer's job, job lock/unlock functions and
macros are added as empty prototypes (nop) in patch 1.
They are converted to use the actual job mutex only in the last
patch. In this way we can freely create locking sections
without worrying about deadlocks with the aiocontext lock.

Patch 2 defines what fields in the job structure need protection.
Patches 3-6 are in preparation to the job locks, moving functions
from global to static and introducing helpers.

Patch 7-9 introduce the (nop) job lock into the job API and
its users, and patches 10-13 categorize respectively locked and unlocked functions in the job API.

Patches 14-17 take care of protecting job->aio_context, and
finally patch 18 makes the prototypes in patch 1 use the
job_mutex and removes all aiocontext lock at the same time.

Tested this series by running unit tests, qemu-iotests and qtests
(x86_64).

This serie is based on my previous series "block layer: split
block APIs in global state and I/O" and also depends on the new
converted tests 141 and 185.

Based-on: <20220121170544.2049944-1-eesposit@redhat.com>
---
v5:
* just restructured patches a little bit better, as there were
  functions used before they were defined.
* rebased on kwolf/block branch and API split serie

v4:
* move "protected by job_mutex" from patch 2 to 15, where the job_mutex is
  actually added.
* s/aio_co_enter/aio_co_schedule in job.c, and adjust tests accordingly.
* remove job_get_aio_context, add job_set_aio_context. Use "fake rwlock"
  to protect job->aiocontext.
* get rid of useless getters method, namely:
  job_get_status
  job_get_pause_count
  job_get_paused
  job_get_busy
  They are all used only by tests, and such getter is pretty useless.
  Replace with job_lock(); assert(); job_unlock();
* use job lock macros instead of job lock/unlock in unit tests.
* convert also blockjob functions to have _locked
* put the job_lock/unlock patches before the _locked ones
* replace aio_co_enter in job.c and detect change of context

v3:
* add "_locked" suffix to the functions called under job_mutex lock
* rename _job_lock in real_job_lock
* job_mutex is now public, and drivers like monitor use it directly
* introduce and protect job_get_aio_context
* remove mirror-specific APIs and just use WITH_JOB_GUARD
* more extensive use of WITH_JOB_GUARD and JOB_LOCK_GUARD

RFC v2:
* use JOB_LOCK_GUARD and WITH_JOB_LOCK_GUARD
* mu(u)ltiple typos in commit messages
* job API split patches are sent separately in another series
* use of empty job_{lock/unlock} and JOB_LOCK_GUARD/WITH_JOB_LOCK_GUARD
  to avoid deadlocks and simplify the reviewer job
* move patch 11 (block_job_query: remove atomic read) as last

Emanuele Giuseppe Esposito (19):
  job.c: make job_mutex and job_lock/unlock() public
  job.h: categorize fields in struct Job
  job.c: API functions not used outside should be static
  job.c: move inner aiocontext lock in callbacks
  aio-wait.h: introduce AIO_WAIT_WHILE_UNLOCKED
  jobs: remove aiocontext locks since the functions are under BQL
  job.h: add _locked duplicates for job API functions called with and
    without job_mutex
  jobs: protect jobs with job_lock/unlock
  jobs: add job lock in find_* functions
  jobs: use job locks also in the unit tests
  block/mirror.c: use of job helpers in drivers to avoid TOC/TOU
  jobs: rename static functions called with job_mutex held
  job.h: rename job API functions called with job_mutex held
  block_job: rename block_job functions called with job_mutex held
  job.h: define unlocked functions
  commit and mirror: create new nodes using bdrv_get_aio_context, and
    not the job aiocontext
  jobs: protect job.aio_context with BQL and job_mutex
  job.c: enable job lock/unlock and remove Aiocontext locks
  block_job_query: remove atomic read

Paolo Bonzini (1):
  job: detect change of aiocontext within job coroutine

 block.c                          |  19 +-
 block/backup.c                   |   4 +-
 block/commit.c                   |   4 +-
 block/mirror.c                   |  21 +-
 block/replication.c              |  10 +-
 blockdev.c                       | 124 +++---
 blockjob.c                       | 132 ++++---
 include/block/aio-wait.h         |  15 +-
 include/block/blockjob.h         |  29 +-
 include/qemu/job.h               | 304 ++++++++++-----
 job-qmp.c                        |  74 ++--
 job.c                            | 648 ++++++++++++++++++-------------
 monitor/qmp-cmds.c               |   7 +-
 qemu-img.c                       |  41 +-
 tests/unit/test-bdrv-drain.c     |  80 ++--
 tests/unit/test-block-iothread.c |   8 +-
 tests/unit/test-blockjob-txn.c   |  32 +-
 tests/unit/test-blockjob.c       | 113 ++++--
 18 files changed, 1001 insertions(+), 664 deletions(-)

-- 
2.31.1

[PATCH v5 01/20] job.c: make job_mutex and job_lock/unlock() public

[Emanuele Giuseppe Esposito]

job mutex will be used to protect the job struct elements and list,
replacing AioContext locks.

Right now use a shared lock for all jobs, in order to keep things
simple. Once the AioContext lock is gone, we can introduce per-job
locks.

To simplify the switch from aiocontext to job lock, introduce
*nop* lock/unlock functions and macros.
We want to always call job_lock/unlock outside the AioContext locks,
and not vice-versa, otherwise we might get a deadlock. This is not
straightforward to do, and that's why we start with nop functions.
Once everything is protected by job_lock/unlock, we can change the nop into
an actual mutex and remove the aiocontext lock.

Since job_mutex is already being used, add static
real_job_{lock/unlock} for the existing usage.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/qemu/job.h | 24 ++++++++++++++++++++++++
 job.c              | 35 +++++++++++++++++++++++------------
 2 files changed, 47 insertions(+), 12 deletions(-)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index c105b31076..d1192ffd61 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -303,6 +303,30 @@ typedef enum JobCreateFlags {
     JOB_MANUAL_DISMISS = 0x04,
 } JobCreateFlags;
 
+extern QemuMutex job_mutex;
+
+#define JOB_LOCK_GUARD() /* QEMU_LOCK_GUARD(&job_mutex) */
+
+#define WITH_JOB_LOCK_GUARD() /* WITH_QEMU_LOCK_GUARD(&job_mutex) */
+
+/**
+ * job_lock:
+ *
+ * Take the mutex protecting the list of jobs and their status.
+ * Most functions called by the monitor need to call job_lock
+ * and job_unlock manually.  On the other hand, function called
+ * by the block jobs themselves and by the block layer will take the
+ * lock for you.
+ */
+void job_lock(void);
+
+/**
+ * job_unlock:
+ *
+ * Release the mutex protecting the list of jobs and their status.
+ */
+void job_unlock(void);
+
 /**
  * Allocate and return a new job transaction. Jobs can be added to the
  * transaction using job_txn_add_job().
diff --git a/job.c b/job.c
index f91cccbed8..d603f9ad1e 100644
--- a/job.c
+++ b/job.c
@@ -32,6 +32,12 @@
 #include "trace/trace-root.h"
 #include "qapi/qapi-events-job.h"
 
+/*
+ * job_mutex protects the jobs list, but also makes the
+ * struct job fields thread-safe.
+ */
+QemuMutex job_mutex;
+
 static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
 
 /* Job State Transition Table */
@@ -74,17 +80,22 @@ struct JobTxn {
     int refcnt;
 };
 
-/* Right now, this mutex is only needed to synchronize accesses to job->busy
- * and job->sleep_timer, such as concurrent calls to job_do_yield and
- * job_enter. */
-static QemuMutex job_mutex;
+void job_lock(void)
+{
+    /* nop */
+}
+
+void job_unlock(void)
+{
+    /* nop */
+}
 
-static void job_lock(void)
+static void real_job_lock(void)
 {
     qemu_mutex_lock(&job_mutex);
 }
 
-static void job_unlock(void)
+static void real_job_unlock(void)
 {
     qemu_mutex_unlock(&job_mutex);
 }
@@ -450,21 +461,21 @@ void job_enter_cond(Job *job, bool(*fn)(Job *job))
         return;
     }
 
-    job_lock();
+    real_job_lock();
     if (job->busy) {
-        job_unlock();
+        real_job_unlock();
         return;
     }
 
     if (fn && !fn(job)) {
-        job_unlock();
+        real_job_unlock();
         return;
     }
 
     assert(!job->deferred_to_main_loop);
     timer_del(&job->sleep_timer);
     job->busy = true;
-    job_unlock();
+    real_job_unlock();
     aio_co_enter(job->aio_context, job->co);
 }
 
@@ -481,13 +492,13 @@ void job_enter(Job *job)
  * called explicitly. */
 static void coroutine_fn job_do_yield(Job *job, uint64_t ns)
 {
-    job_lock();
+    real_job_lock();
     if (ns != -1) {
         timer_mod(&job->sleep_timer, ns);
     }
     job->busy = false;
     job_event_idle(job);
-    job_unlock();
+    real_job_unlock();
     qemu_coroutine_yield();
 
     /* Set by job_enter_cond() before re-entering the coroutine.  */
-- 
2.31.1

Re: [PATCH v5 01/20] job.c: make job_mutex and job_lock/unlock() public

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1197 bytes --]

On Tue, Feb 08, 2022 at 09:34:54AM -0500, Emanuele Giuseppe Esposito wrote:
> job mutex will be used to protect the job struct elements and list,
> replacing AioContext locks.
> 
> Right now use a shared lock for all jobs, in order to keep things
> simple. Once the AioContext lock is gone, we can introduce per-job
> locks.
> 
> To simplify the switch from aiocontext to job lock, introduce
> *nop* lock/unlock functions and macros.
> We want to always call job_lock/unlock outside the AioContext locks,
> and not vice-versa, otherwise we might get a deadlock. This is not
> straightforward to do, and that's why we start with nop functions.
> Once everything is protected by job_lock/unlock, we can change the nop into
> an actual mutex and remove the aiocontext lock.
> 
> Since job_mutex is already being used, add static
> real_job_{lock/unlock} for the existing usage.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  include/qemu/job.h | 24 ++++++++++++++++++++++++
>  job.c              | 35 +++++++++++++++++++++++------------
>  2 files changed, 47 insertions(+), 12 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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[PATCH v5 02/20] job.h: categorize fields in struct Job

[Emanuele Giuseppe Esposito]

Categorize the fields in struct Job to understand which ones
need to be protected by the job mutex and which don't.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/qemu/job.h | 59 ++++++++++++++++++++++++++--------------------
 1 file changed, 34 insertions(+), 25 deletions(-)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index d1192ffd61..86ec46c09e 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -40,27 +40,50 @@ typedef struct JobTxn JobTxn;
  * Long-running operation.
  */
 typedef struct Job {
+
+    /* Fields set at initialization (job_create), and never modified */
+
     /** The ID of the job. May be NULL for internal jobs. */
     char *id;
 
-    /** The type of this job. */
+    /**
+     * The type of this job.
+     * All callbacks are called with job_mutex *not* held.
+     */
     const JobDriver *driver;
 
-    /** Reference count of the block job */
-    int refcnt;
-
-    /** Current state; See @JobStatus for details. */
-    JobStatus status;
-
-    /** AioContext to run the job coroutine in */
-    AioContext *aio_context;
-
     /**
      * The coroutine that executes the job.  If not NULL, it is reentered when
      * busy is false and the job is cancelled.
+     * Initialized in job_start()
      */
     Coroutine *co;
 
+    /** True if this job should automatically finalize itself */
+    bool auto_finalize;
+
+    /** True if this job should automatically dismiss itself */
+    bool auto_dismiss;
+
+    /** The completion function that will be called when the job completes.  */
+    BlockCompletionFunc *cb;
+
+    /** The opaque value that is passed to the completion function.  */
+    void *opaque;
+
+    /* ProgressMeter API is thread-safe */
+    ProgressMeter progress;
+
+
+    /** AioContext to run the job coroutine in */
+    AioContext *aio_context;
+
+    /** Reference count of the block job */
+    int refcnt;
+
+    /** Current state; See @JobStatus for details. */
+    JobStatus status;
+
     /**
      * Timer that is used by @job_sleep_ns. Accessed under job_mutex (in
      * job.c).
@@ -112,14 +135,6 @@ typedef struct Job {
     /** Set to true when the job has deferred work to the main loop. */
     bool deferred_to_main_loop;
 
-    /** True if this job should automatically finalize itself */
-    bool auto_finalize;
-
-    /** True if this job should automatically dismiss itself */
-    bool auto_dismiss;
-
-    ProgressMeter progress;
-
     /**
      * Return code from @run and/or @prepare callback(s).
      * Not final until the job has reached the CONCLUDED status.
@@ -134,12 +149,6 @@ typedef struct Job {
      */
     Error *err;
 
-    /** The completion function that will be called when the job completes.  */
-    BlockCompletionFunc *cb;
-
-    /** The opaque value that is passed to the completion function.  */
-    void *opaque;
-
     /** Notifiers called when a cancelled job is finalised */
     NotifierList on_finalize_cancelled;
 
@@ -167,6 +176,7 @@ typedef struct Job {
 
 /**
  * Callbacks and other information about a Job driver.
+ * All callbacks are invoked with job_mutex *not* held.
  */
 struct JobDriver {
 
@@ -472,7 +482,6 @@ void job_yield(Job *job);
  */
 void coroutine_fn job_sleep_ns(Job *job, int64_t ns);
 
-
 /** Returns the JobType of a given Job. */
 JobType job_type(const Job *job);
 
-- 
2.31.1

Re: [PATCH v5 02/20] job.h: categorize fields in struct Job

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 868 bytes --]

On Tue, Feb 08, 2022 at 09:34:55AM -0500, Emanuele Giuseppe Esposito wrote:
> Categorize the fields in struct Job to understand which ones
> need to be protected by the job mutex and which don't.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  include/qemu/job.h | 59 ++++++++++++++++++++++++++--------------------
>  1 file changed, 34 insertions(+), 25 deletions(-)
> 
> diff --git a/include/qemu/job.h b/include/qemu/job.h
> index d1192ffd61..86ec46c09e 100644
> --- a/include/qemu/job.h
> +++ b/include/qemu/job.h
> @@ -40,27 +40,50 @@ typedef struct JobTxn JobTxn;
>   * Long-running operation.
>   */
>  typedef struct Job {
> +
> +    /* Fields set at initialization (job_create), and never modified */

Is there a corresponding "Field protected by job_mutex" comment that
separates fields that need locking?

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Re: [PATCH v5 02/20] job.h: categorize fields in struct Job

[Emanuele Giuseppe Esposito]

On 10/02/2022 16:40, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:34:55AM -0500, Emanuele Giuseppe Esposito wrote:
>> Categorize the fields in struct Job to understand which ones
>> need to be protected by the job mutex and which don't.
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>  include/qemu/job.h | 59 ++++++++++++++++++++++++++--------------------
>>  1 file changed, 34 insertions(+), 25 deletions(-)
>>
>> diff --git a/include/qemu/job.h b/include/qemu/job.h
>> index d1192ffd61..86ec46c09e 100644
>> --- a/include/qemu/job.h
>> +++ b/include/qemu/job.h
>> @@ -40,27 +40,50 @@ typedef struct JobTxn JobTxn;
>>   * Long-running operation.
>>   */
>>  typedef struct Job {
>> +
>> +    /* Fields set at initialization (job_create), and never modified */
> 
> Is there a corresponding "Field protected by job_mutex" comment that
> separates fields that need locking?
> 

That would be the comment

    /** Protected by job_mutex */

situated right after the field "ProgressMeter progress;".

Do you want me to change it in "Fields protected by job_mutex"?

Thank you,
Emanuele

Re: [PATCH v5 02/20] job.h: categorize fields in struct Job

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1693 bytes --]

On Thu, Feb 10, 2022 at 05:26:52PM +0100, Emanuele Giuseppe Esposito wrote:
> 
> 
> On 10/02/2022 16:40, Stefan Hajnoczi wrote:
> > On Tue, Feb 08, 2022 at 09:34:55AM -0500, Emanuele Giuseppe Esposito wrote:
> >> Categorize the fields in struct Job to understand which ones
> >> need to be protected by the job mutex and which don't.
> >>
> >> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> >> ---
> >>  include/qemu/job.h | 59 ++++++++++++++++++++++++++--------------------
> >>  1 file changed, 34 insertions(+), 25 deletions(-)
> >>
> >> diff --git a/include/qemu/job.h b/include/qemu/job.h
> >> index d1192ffd61..86ec46c09e 100644
> >> --- a/include/qemu/job.h
> >> +++ b/include/qemu/job.h
> >> @@ -40,27 +40,50 @@ typedef struct JobTxn JobTxn;
> >>   * Long-running operation.
> >>   */
> >>  typedef struct Job {
> >> +
> >> +    /* Fields set at initialization (job_create), and never modified */
> > 
> > Is there a corresponding "Field protected by job_mutex" comment that
> > separates fields that need locking?
> > 
> 
> That would be the comment
> 
>     /** Protected by job_mutex */
> 
> situated right after the field "ProgressMeter progress;".
> 
> Do you want me to change it in "Fields protected by job_mutex"?

I don't see it:

+    /** The opaque value that is passed to the completion function.  */
+    void *opaque;
+
+    /* ProgressMeter API is thread-safe */
+    ProgressMeter progress;
+
+
+    /** AioContext to run the job coroutine in */
+    AioContext *aio_context;
+
+    /** Reference count of the block job */
+    int refcnt;

Is it added by a later patch or did I miss it?

Stefan

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Re: [PATCH v5 02/20] job.h: categorize fields in struct Job

[Emanuele Giuseppe Esposito]

On 10/02/2022 18:35, Stefan Hajnoczi wrote:
> On Thu, Feb 10, 2022 at 05:26:52PM +0100, Emanuele Giuseppe Esposito wrote:
>>
>>
>> On 10/02/2022 16:40, Stefan Hajnoczi wrote:
>>> On Tue, Feb 08, 2022 at 09:34:55AM -0500, Emanuele Giuseppe Esposito wrote:
>>>> Categorize the fields in struct Job to understand which ones
>>>> need to be protected by the job mutex and which don't.
>>>>
>>>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>>>> ---
>>>>  include/qemu/job.h | 59 ++++++++++++++++++++++++++--------------------
>>>>  1 file changed, 34 insertions(+), 25 deletions(-)
>>>>
>>>> diff --git a/include/qemu/job.h b/include/qemu/job.h
>>>> index d1192ffd61..86ec46c09e 100644
>>>> --- a/include/qemu/job.h
>>>> +++ b/include/qemu/job.h
>>>> @@ -40,27 +40,50 @@ typedef struct JobTxn JobTxn;
>>>>   * Long-running operation.
>>>>   */
>>>>  typedef struct Job {
>>>> +
>>>> +    /* Fields set at initialization (job_create), and never modified */
>>>
>>> Is there a corresponding "Field protected by job_mutex" comment that
>>> separates fields that need locking?
>>>
>>
>> That would be the comment
>>
>>     /** Protected by job_mutex */
>>
>> situated right after the field "ProgressMeter progress;".
>>
>> Do you want me to change it in "Fields protected by job_mutex"?
> 
> I don't see it:
> 
> +    /** The opaque value that is passed to the completion function.  */
> +    void *opaque;
> +
> +    /* ProgressMeter API is thread-safe */
> +    ProgressMeter progress;
> +
> +
> +    /** AioContext to run the job coroutine in */
> +    AioContext *aio_context;
> +
> +    /** Reference count of the block job */
> +    int refcnt;
> 
> Is it added by a later patch or did I miss it?
> 

Yes sorry I forgot: it is added in patch 19, when the lock is not a nop
anymore.

I think this was suggested in one of the previous reviews, to avoid
having a misleading comment when the fields are not yet protected.

Emanuele

[PATCH v5 03/20] job.c: API functions not used outside should be static

[Emanuele Giuseppe Esposito]

job_event_* functions can all be static, as they are not used
outside job.c.

Same applies for job_txn_add_job().

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/qemu/job.h | 18 ------------------
 job.c              | 12 +++++++++---
 2 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index 86ec46c09e..6000463126 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -356,18 +356,6 @@ JobTxn *job_txn_new(void);
  */
 void job_txn_unref(JobTxn *txn);
 
-/**
- * @txn: The transaction (may be NULL)
- * @job: Job to add to the transaction
- *
- * Add @job to the transaction.  The @job must not already be in a transaction.
- * The caller must call either job_txn_unref() or job_completed() to release
- * the reference that is automatically grabbed here.
- *
- * If @txn is NULL, the function does nothing.
- */
-void job_txn_add_job(JobTxn *txn, Job *job);
-
 /**
  * Create a new long-running job and return it.
  *
@@ -429,12 +417,6 @@ void job_progress_set_remaining(Job *job, uint64_t remaining);
  */
 void job_progress_increase_remaining(Job *job, uint64_t delta);
 
-/** To be called when a cancelled job is finalised. */
-void job_event_cancelled(Job *job);
-
-/** To be called when a successfully completed job is finalised. */
-void job_event_completed(Job *job);
-
 /**
  * Conditionally enter the job coroutine if the job is ready to run, not
  * already busy and fn() returns true. fn() is called while under the job_lock
diff --git a/job.c b/job.c
index d603f9ad1e..f13939d3c6 100644
--- a/job.c
+++ b/job.c
@@ -125,7 +125,7 @@ void job_txn_unref(JobTxn *txn)
     }
 }
 
-void job_txn_add_job(JobTxn *txn, Job *job)
+static void job_txn_add_job(JobTxn *txn, Job *job)
 {
     if (!txn) {
         return;
@@ -427,12 +427,18 @@ void job_progress_increase_remaining(Job *job, uint64_t delta)
     progress_increase_remaining(&job->progress, delta);
 }
 
-void job_event_cancelled(Job *job)
+/**
+ * To be called when a cancelled job is finalised.
+ */
+static void job_event_cancelled(Job *job)
 {
     notifier_list_notify(&job->on_finalize_cancelled, job);
 }
 
-void job_event_completed(Job *job)
+/**
+ * To be called when a successfully completed job is finalised.
+ */
+static void job_event_completed(Job *job)
 {
     notifier_list_notify(&job->on_finalize_completed, job);
 }
-- 
2.31.1

Re: [PATCH v5 03/20] job.c: API functions not used outside should be static

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1454 bytes --]

On Tue, Feb 08, 2022 at 09:34:56AM -0500, Emanuele Giuseppe Esposito wrote:
> job_event_* functions can all be static, as they are not used
> outside job.c.
> 
> Same applies for job_txn_add_job().
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  include/qemu/job.h | 18 ------------------
>  job.c              | 12 +++++++++---
>  2 files changed, 9 insertions(+), 21 deletions(-)
> 
> diff --git a/include/qemu/job.h b/include/qemu/job.h
> index 86ec46c09e..6000463126 100644
> --- a/include/qemu/job.h
> +++ b/include/qemu/job.h
> @@ -356,18 +356,6 @@ JobTxn *job_txn_new(void);
>   */
>  void job_txn_unref(JobTxn *txn);
>  
> -/**
> - * @txn: The transaction (may be NULL)
> - * @job: Job to add to the transaction
> - *
> - * Add @job to the transaction.  The @job must not already be in a transaction.
> - * The caller must call either job_txn_unref() or job_completed() to release
> - * the reference that is automatically grabbed here.
> - *
> - * If @txn is NULL, the function does nothing.
> - */
> -void job_txn_add_job(JobTxn *txn, Job *job);
...
> diff --git a/job.c b/job.c
> index d603f9ad1e..f13939d3c6 100644
> --- a/job.c
> +++ b/job.c
> @@ -125,7 +125,7 @@ void job_txn_unref(JobTxn *txn)
>      }
>  }
>  
> -void job_txn_add_job(JobTxn *txn, Job *job)
> +static void job_txn_add_job(JobTxn *txn, Job *job)

Please move the doc comments into the .c file too.

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[PATCH v5 04/20] job.c: move inner aiocontext lock in callbacks

[Emanuele Giuseppe Esposito]

Instead of having the lock in job_tnx_apply, move it inside
in the callback. This will be helpful for next commits, when
we introduce job_lock/unlock pairs.

job_transition_to_pending() and job_needs_finalize() do not
need to be protected by the aiocontext lock.

No functional change intended.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 job.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/job.c b/job.c
index f13939d3c6..d8c13ac0d1 100644
--- a/job.c
+++ b/job.c
@@ -149,7 +149,6 @@ static void job_txn_del_job(Job *job)
 
 static int job_txn_apply(Job *job, int fn(Job *))
 {
-    AioContext *inner_ctx;
     Job *other_job, *next;
     JobTxn *txn = job->txn;
     int rc = 0;
@@ -164,10 +163,7 @@ static int job_txn_apply(Job *job, int fn(Job *))
     aio_context_release(job->aio_context);
 
     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
-        inner_ctx = other_job->aio_context;
-        aio_context_acquire(inner_ctx);
         rc = fn(other_job);
-        aio_context_release(inner_ctx);
         if (rc) {
             break;
         }
@@ -717,11 +713,15 @@ static void job_clean(Job *job)
 
 static int job_finalize_single(Job *job)
 {
+    AioContext *ctx = job->aio_context;
+
     assert(job_is_completed(job));
 
     /* Ensure abort is called for late-transactional failures */
     job_update_rc(job);
 
+    aio_context_acquire(ctx);
+
     if (!job->ret) {
         job_commit(job);
     } else {
@@ -729,6 +729,8 @@ static int job_finalize_single(Job *job)
     }
     job_clean(job);
 
+    aio_context_release(ctx);
+
     if (job->cb) {
         job->cb(job->opaque, job->ret);
     }
@@ -833,8 +835,8 @@ static void job_completed_txn_abort(Job *job)
             assert(job_cancel_requested(other_job));
             job_finish_sync(other_job, NULL, NULL);
         }
-        job_finalize_single(other_job);
         aio_context_release(ctx);
+        job_finalize_single(other_job);
     }
 
     /*
@@ -849,11 +851,16 @@ static void job_completed_txn_abort(Job *job)
 
 static int job_prepare(Job *job)
 {
+    AioContext *ctx = job->aio_context;
     assert(qemu_in_main_thread());
+
     if (job->ret == 0 && job->driver->prepare) {
+        aio_context_acquire(ctx);
         job->ret = job->driver->prepare(job);
+        aio_context_release(ctx);
         job_update_rc(job);
     }
+
     return job->ret;
 }
 
-- 
2.31.1

Re: [PATCH v5 04/20] job.c: move inner aiocontext lock in callbacks

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 3166 bytes --]

On Tue, Feb 08, 2022 at 09:34:57AM -0500, Emanuele Giuseppe Esposito wrote:
> Instead of having the lock in job_tnx_apply, move it inside

s/tnx/txn/

> in the callback. This will be helpful for next commits, when
> we introduce job_lock/unlock pairs.
> 
> job_transition_to_pending() and job_needs_finalize() do not
> need to be protected by the aiocontext lock.
> 
> No functional change intended.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  job.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)

I find this hard to review. The patch reduces the scope of the
AioContext lock region and accesses Job in places where the AioContext
was previously held. The commit description doesn't explain why it is
safe to do this.

I may need to audit the code myself but will try reviewing a few more
patches first to see if I get the hang of this.

> 
> diff --git a/job.c b/job.c
> index f13939d3c6..d8c13ac0d1 100644
> --- a/job.c
> +++ b/job.c
> @@ -149,7 +149,6 @@ static void job_txn_del_job(Job *job)
>  
>  static int job_txn_apply(Job *job, int fn(Job *))
>  {
> -    AioContext *inner_ctx;
>      Job *other_job, *next;
>      JobTxn *txn = job->txn;
>      int rc = 0;
> @@ -164,10 +163,7 @@ static int job_txn_apply(Job *job, int fn(Job *))
>      aio_context_release(job->aio_context);
>  
>      QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
> -        inner_ctx = other_job->aio_context;
> -        aio_context_acquire(inner_ctx);
>          rc = fn(other_job);
> -        aio_context_release(inner_ctx);
>          if (rc) {
>              break;
>          }
> @@ -717,11 +713,15 @@ static void job_clean(Job *job)
>  
>  static int job_finalize_single(Job *job)
>  {
> +    AioContext *ctx = job->aio_context;
> +
>      assert(job_is_completed(job));
>  
>      /* Ensure abort is called for late-transactional failures */
>      job_update_rc(job);
>  
> +    aio_context_acquire(ctx);
> +
>      if (!job->ret) {
>          job_commit(job);
>      } else {
> @@ -729,6 +729,8 @@ static int job_finalize_single(Job *job)
>      }
>      job_clean(job);
>  
> +    aio_context_release(ctx);
> +
>      if (job->cb) {
>          job->cb(job->opaque, job->ret);
>      }
> @@ -833,8 +835,8 @@ static void job_completed_txn_abort(Job *job)
>              assert(job_cancel_requested(other_job));
>              job_finish_sync(other_job, NULL, NULL);
>          }
> -        job_finalize_single(other_job);
>          aio_context_release(ctx);
> +        job_finalize_single(other_job);
>      }
>  
>      /*
> @@ -849,11 +851,16 @@ static void job_completed_txn_abort(Job *job)
>  
>  static int job_prepare(Job *job)
>  {
> +    AioContext *ctx = job->aio_context;
>      assert(qemu_in_main_thread());
> +
>      if (job->ret == 0 && job->driver->prepare) {
> +        aio_context_acquire(ctx);
>          job->ret = job->driver->prepare(job);
> +        aio_context_release(ctx);
>          job_update_rc(job);
>      }
> +
>      return job->ret;
>  }
>  
> -- 
> 2.31.1
> 

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Re: [PATCH v5 04/20] job.c: move inner aiocontext lock in callbacks

[Emanuele Giuseppe Esposito]

On 17/02/2022 14:45, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:34:57AM -0500, Emanuele Giuseppe Esposito wrote:
>> Instead of having the lock in job_tnx_apply, move it inside
> 
> s/tnx/txn/
> 
>> in the callback. This will be helpful for next commits, when
>> we introduce job_lock/unlock pairs.
>>
>> job_transition_to_pending() and job_needs_finalize() do not
>> need to be protected by the aiocontext lock.
>>
>> No functional change intended.
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>  job.c | 17 ++++++++++++-----
>>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> I find this hard to review. The patch reduces the scope of the
> AioContext lock region and accesses Job in places where the AioContext
> was previously held. The commit description doesn't explain why it is
> safe to do this.

I will add this to the commit description, but in my opinion the
AioContext lock was not protecting any of the job fields in this patch.

It is only taken because the callbacks assume it is always held.
No job field in this patch is protected by the AioContext lock because
they are also read/written in functions that never take the lock.

Emanuele
> 
> I may need to audit the code myself but will try reviewing a few more
> patches first to see if I get the hang of this.
> 
>>
>> diff --git a/job.c b/job.c
>> index f13939d3c6..d8c13ac0d1 100644
>> --- a/job.c
>> +++ b/job.c
>> @@ -149,7 +149,6 @@ static void job_txn_del_job(Job *job)
>>  
>>  static int job_txn_apply(Job *job, int fn(Job *))
>>  {
>> -    AioContext *inner_ctx;
>>      Job *other_job, *next;
>>      JobTxn *txn = job->txn;
>>      int rc = 0;
>> @@ -164,10 +163,7 @@ static int job_txn_apply(Job *job, int fn(Job *))
>>      aio_context_release(job->aio_context);
>>  
>>      QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
>> -        inner_ctx = other_job->aio_context;
>> -        aio_context_acquire(inner_ctx);
>>          rc = fn(other_job);
>> -        aio_context_release(inner_ctx);
>>          if (rc) {
>>              break;
>>          }
>> @@ -717,11 +713,15 @@ static void job_clean(Job *job)
>>  
>>  static int job_finalize_single(Job *job)
>>  {
>> +    AioContext *ctx = job->aio_context;
>> +
>>      assert(job_is_completed(job));
>>  
>>      /* Ensure abort is called for late-transactional failures */
>>      job_update_rc(job);
>>  
>> +    aio_context_acquire(ctx);
>> +
>>      if (!job->ret) {
>>          job_commit(job);
>>      } else {
>> @@ -729,6 +729,8 @@ static int job_finalize_single(Job *job)
>>      }
>>      job_clean(job);
>>  
>> +    aio_context_release(ctx);
>> +
>>      if (job->cb) {
>>          job->cb(job->opaque, job->ret);
>>      }
>> @@ -833,8 +835,8 @@ static void job_completed_txn_abort(Job *job)
>>              assert(job_cancel_requested(other_job));
>>              job_finish_sync(other_job, NULL, NULL);
>>          }
>> -        job_finalize_single(other_job);
>>          aio_context_release(ctx);
>> +        job_finalize_single(other_job);
>>      }
>>  
>>      /*
>> @@ -849,11 +851,16 @@ static void job_completed_txn_abort(Job *job)
>>  
>>  static int job_prepare(Job *job)
>>  {
>> +    AioContext *ctx = job->aio_context;
>>      assert(qemu_in_main_thread());
>> +
>>      if (job->ret == 0 && job->driver->prepare) {
>> +        aio_context_acquire(ctx);
>>          job->ret = job->driver->prepare(job);
>> +        aio_context_release(ctx);
>>          job_update_rc(job);
>>      }
>> +
>>      return job->ret;
>>  }
>>  
>> -- 
>> 2.31.1
>>

Re: [PATCH v5 04/20] job.c: move inner aiocontext lock in callbacks

[Emanuele Giuseppe Esposito]

On 17/02/2022 14:45, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:34:57AM -0500, Emanuele Giuseppe Esposito wrote:
>> Instead of having the lock in job_tnx_apply, move it inside
> 
> s/tnx/txn/
> 
>> in the callback. This will be helpful for next commits, when
>> we introduce job_lock/unlock pairs.
>>
>> job_transition_to_pending() and job_needs_finalize() do not
>> need to be protected by the aiocontext lock.
>>
>> No functional change intended.
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>  job.c | 17 ++++++++++++-----
>>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> I find this hard to review. The patch reduces the scope of the
> AioContext lock region and accesses Job in places where the AioContext
> was previously held. The commit description doesn't explain why it is
> safe to do this.
> 
> I may need to audit the code myself but will try reviewing a few more
> patches first to see if I get the hang of this.
> 
>>
>> diff --git a/job.c b/job.c
>> index f13939d3c6..d8c13ac0d1 100644
>> --- a/job.c
>> +++ b/job.c
>> @@ -149,7 +149,6 @@ static void job_txn_del_job(Job *job)
>>  
>>  static int job_txn_apply(Job *job, int fn(Job *))
>>  {
>> -    AioContext *inner_ctx;
>>      Job *other_job, *next;
>>      JobTxn *txn = job->txn;
>>      int rc = 0;
>> @@ -164,10 +163,7 @@ static int job_txn_apply(Job *job, int fn(Job *))
>>      aio_context_release(job->aio_context);
>>  
>>      QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
>> -        inner_ctx = other_job->aio_context;
>> -        aio_context_acquire(inner_ctx);
>>          rc = fn(other_job);
>> -        aio_context_release(inner_ctx);
>>          if (rc) {
>>              break;
>>          }
>> @@ -717,11 +713,15 @@ static void job_clean(Job *job)
>>  
>>  static int job_finalize_single(Job *job)
>>  {
>> +    AioContext *ctx = job->aio_context;
>> +
>>      assert(job_is_completed(job));
>>  
>>      /* Ensure abort is called for late-transactional failures */
>>      job_update_rc(job);
>>  
>> +    aio_context_acquire(ctx);
>> +
>>      if (!job->ret) {
>>          job_commit(job);
>>      } else {
>> @@ -729,6 +729,8 @@ static int job_finalize_single(Job *job)
>>      }
>>      job_clean(job);
>>  
>> +    aio_context_release(ctx);
>> +
>>      if (job->cb) {
>>          job->cb(job->opaque, job->ret);
>>      }
>> @@ -833,8 +835,8 @@ static void job_completed_txn_abort(Job *job)
>>              assert(job_cancel_requested(other_job));
>>              job_finish_sync(other_job, NULL, NULL);
>>          }
>> -        job_finalize_single(other_job);
>>          aio_context_release(ctx);
>> +        job_finalize_single(other_job);
>>      }
>>  
>>      /*
>> @@ -849,11 +851,16 @@ static void job_completed_txn_abort(Job *job)
>>  
>>  static int job_prepare(Job *job)
>>  {
>> +    AioContext *ctx = job->aio_context;
>>      assert(qemu_in_main_thread());
>> +
>>      if (job->ret == 0 && job->driver->prepare) {
>> +        aio_context_acquire(ctx);
>>          job->ret = job->driver->prepare(job);
>> +        aio_context_release(ctx);
>>          job_update_rc(job);
>>      }
>> +
>>      return job->ret;
>>  }
>>  
>> -- 
>> 2.31.1
>>

Maybe just for safety this should also go in patch 19, where I enable
job lock/unlock and reduce/remove AioContext locks.

Emanuele

[PATCH v5 05/20] aio-wait.h: introduce AIO_WAIT_WHILE_UNLOCKED

[Emanuele Giuseppe Esposito]

Same as AIO_WAIT_WHILE macro, but if we are in the Main loop
do not release and then acquire ctx_ 's aiocontext.

Once all Aiocontext locks go away, this macro will replace
AIO_WAIT_WHILE.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/block/aio-wait.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
index b39eefb38d..ff27fe4eab 100644
--- a/include/block/aio-wait.h
+++ b/include/block/aio-wait.h
@@ -59,10 +59,11 @@ typedef struct {
 extern AioWait global_aio_wait;
 
 /**
- * AIO_WAIT_WHILE:
+ * _AIO_WAIT_WHILE:
  * @ctx: the aio context, or NULL if multiple aio contexts (for which the
  *       caller does not hold a lock) are involved in the polling condition.
  * @cond: wait while this conditional expression is true
+ * @unlock: whether to unlock and then lock again @ctx
  *
  * Wait while a condition is true.  Use this to implement synchronous
  * operations that require event loop activity.
@@ -75,7 +76,7 @@ extern AioWait global_aio_wait;
  * wait on conditions between two IOThreads since that could lead to deadlock,
  * go via the main loop instead.
  */
-#define AIO_WAIT_WHILE(ctx, cond) ({                               \
+#define _AIO_WAIT_WHILE(ctx, cond, unlock) ({                      \
     bool waited_ = false;                                          \
     AioWait *wait_ = &global_aio_wait;                             \
     AioContext *ctx_ = (ctx);                                      \
@@ -90,11 +91,11 @@ extern AioWait global_aio_wait;
         assert(qemu_get_current_aio_context() ==                   \
                qemu_get_aio_context());                            \
         while ((cond)) {                                           \
-            if (ctx_) {                                            \
+            if (unlock && ctx_) {                                  \
                 aio_context_release(ctx_);                         \
             }                                                      \
             aio_poll(qemu_get_aio_context(), true);                \
-            if (ctx_) {                                            \
+            if (unlock && ctx_) {                                  \
                 aio_context_acquire(ctx_);                         \
             }                                                      \
             waited_ = true;                                        \
@@ -103,6 +104,12 @@ extern AioWait global_aio_wait;
     qatomic_dec(&wait_->num_waiters);                              \
     waited_; })
 
+#define AIO_WAIT_WHILE(ctx, cond)                                  \
+    _AIO_WAIT_WHILE(ctx, cond, true)
+
+#define AIO_WAIT_WHILE_UNLOCKED(ctx, cond)                         \
+    _AIO_WAIT_WHILE(ctx, cond, false)
+
 /**
  * aio_wait_kick:
  * Wake up the main thread if it is waiting on AIO_WAIT_WHILE().  During
-- 
2.31.1

Re: [PATCH v5 05/20] aio-wait.h: introduce AIO_WAIT_WHILE_UNLOCKED

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1186 bytes --]

On Tue, Feb 08, 2022 at 09:34:58AM -0500, Emanuele Giuseppe Esposito wrote:
> Same as AIO_WAIT_WHILE macro, but if we are in the Main loop
> do not release and then acquire ctx_ 's aiocontext.
> 
> Once all Aiocontext locks go away, this macro will replace
> AIO_WAIT_WHILE.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  include/block/aio-wait.h | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
> index b39eefb38d..ff27fe4eab 100644
> --- a/include/block/aio-wait.h
> +++ b/include/block/aio-wait.h
> @@ -59,10 +59,11 @@ typedef struct {
>  extern AioWait global_aio_wait;
>  
>  /**
> - * AIO_WAIT_WHILE:
> + * _AIO_WAIT_WHILE:
>   * @ctx: the aio context, or NULL if multiple aio contexts (for which the
>   *       caller does not hold a lock) are involved in the polling condition.
>   * @cond: wait while this conditional expression is true
> + * @unlock: whether to unlock and then lock again @ctx

Please document that this only applies when waiting for another
AioContext from the main loop thread. It's ignored otherwise.

[-- Attachment #2: signature.asc --]
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[PATCH v5 06/20] jobs: remove aiocontext locks since the functions are under BQL

[Emanuele Giuseppe Esposito]

In preparation to the job_lock/unlock patch, remove these
aiocontext locks.
The main reason these two locks are removed here is because
they are inside a loop iterating on the jobs list. Once the
job_lock is added, it will have to protect the whole loop,
wrapping also the aiocontext acquire/release.

We don't want this, as job_lock must be taken inside the AioContext
lock, and taking it outside would cause deadlocks.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 blockdev.c | 4 ----
 job-qmp.c  | 4 ----
 2 files changed, 8 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 8cac3d739c..e315466914 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3713,15 +3713,11 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
 
     for (job = block_job_next(NULL); job; job = block_job_next(job)) {
         BlockJobInfo *value;
-        AioContext *aio_context;
 
         if (block_job_is_internal(job)) {
             continue;
         }
-        aio_context = block_job_get_aio_context(job);
-        aio_context_acquire(aio_context);
         value = block_job_query(job, errp);
-        aio_context_release(aio_context);
         if (!value) {
             qapi_free_BlockJobInfoList(head);
             return NULL;
diff --git a/job-qmp.c b/job-qmp.c
index 829a28aa70..a6774aaaa5 100644
--- a/job-qmp.c
+++ b/job-qmp.c
@@ -173,15 +173,11 @@ JobInfoList *qmp_query_jobs(Error **errp)
 
     for (job = job_next(NULL); job; job = job_next(job)) {
         JobInfo *value;
-        AioContext *aio_context;
 
         if (job_is_internal(job)) {
             continue;
         }
-        aio_context = job->aio_context;
-        aio_context_acquire(aio_context);
         value = job_query_single(job, errp);
-        aio_context_release(aio_context);
         if (!value) {
             qapi_free_JobInfoList(head);
             return NULL;
-- 
2.31.1

Re: [PATCH v5 06/20] jobs: remove aiocontext locks since the functions are under BQL

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1678 bytes --]

On Tue, Feb 08, 2022 at 09:34:59AM -0500, Emanuele Giuseppe Esposito wrote:
> In preparation to the job_lock/unlock patch, remove these
> aiocontext locks.
> The main reason these two locks are removed here is because
> they are inside a loop iterating on the jobs list. Once the
> job_lock is added, it will have to protect the whole loop,
> wrapping also the aiocontext acquire/release.
> 
> We don't want this, as job_lock must be taken inside the AioContext
> lock, and taking it outside would cause deadlocks.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  blockdev.c | 4 ----
>  job-qmp.c  | 4 ----
>  2 files changed, 8 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 8cac3d739c..e315466914 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3713,15 +3713,11 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
>  
>      for (job = block_job_next(NULL); job; job = block_job_next(job)) {

I'm confused. block_job_next() is supposed to be called with job_mutex
held since it iterates the jobs list.

The patch series might fix this later on but it's hard to review patches
with broken invariants.

Does this mean git-bisect(1) is broken since intermediate commits are
not thread-safe?

>          BlockJobInfo *value;
> -        AioContext *aio_context;
>  
>          if (block_job_is_internal(job)) {
>              continue;
>          }
> -        aio_context = block_job_get_aio_context(job);
> -        aio_context_acquire(aio_context);
>          value = block_job_query(job, errp);

This function accesses fields that are protected by job_mutex, which we
don't hold.

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Re: [PATCH v5 06/20] jobs: remove aiocontext locks since the functions are under BQL

[Emanuele Giuseppe Esposito]

On 17/02/2022 15:12, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:34:59AM -0500, Emanuele Giuseppe Esposito wrote:
>> In preparation to the job_lock/unlock patch, remove these
>> aiocontext locks.
>> The main reason these two locks are removed here is because
>> they are inside a loop iterating on the jobs list. Once the
>> job_lock is added, it will have to protect the whole loop,
>> wrapping also the aiocontext acquire/release.
>>
>> We don't want this, as job_lock must be taken inside the AioContext
>> lock, and taking it outside would cause deadlocks.
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>  blockdev.c | 4 ----
>>  job-qmp.c  | 4 ----
>>  2 files changed, 8 deletions(-)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 8cac3d739c..e315466914 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -3713,15 +3713,11 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
>>  
>>      for (job = block_job_next(NULL); job; job = block_job_next(job)) {
> 
> I'm confused. block_job_next() is supposed to be called with job_mutex
> held since it iterates the jobs list.

Ok here it is clear that the lock is taken to protect the list. So I
should squash this patch with the one that enables job lock/unlock
(patch 19).

Emanuele

> 
> The patch series might fix this later on but it's hard to review patches
> with broken invariants.
> 
> Does this mean git-bisect(1) is broken since intermediate commits are
> not thread-safe?
> 
>>          BlockJobInfo *value;
>> -        AioContext *aio_context;
>>  
>>          if (block_job_is_internal(job)) {
>>              continue;
>>          }
>> -        aio_context = block_job_get_aio_context(job);
>> -        aio_context_acquire(aio_context);
>>          value = block_job_query(job, errp);
> 
> This function accesses fields that are protected by job_mutex, which we
> don't hold.
> 

[PATCH v5 07/20] job.h: add _locked duplicates for job API functions called with and without job_mutex

[Emanuele Giuseppe Esposito]

In preparation to the job_lock/unlock usage, create _locked
duplicates of some functions, since they will be sometimes called with
job_mutex held (mostly within job.c),
and sometimes without (mostly from JobDrivers using the job API).

Therefore create a _locked version of such function, so that it
can be used in both cases.

List of functions duplicated as _locked:
job_is_ready (both versions are public)
job_is_completed (both versions are public)
job_is_cancelled (_locked version is public, needed by mirror.c)
job_pause_point (_locked version is static, purely done to simplify the code)
job_cancel_requested (_locked version is static)

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 include/qemu/job.h | 25 +++++++++++++++++++++---
 job.c              | 48 ++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 64 insertions(+), 9 deletions(-)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index 6000463126..aa33d091b1 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -473,21 +473,40 @@ const char *job_type_str(const Job *job);
 /** Returns true if the job should not be visible to the management layer. */
 bool job_is_internal(Job *job);
 
-/** Returns whether the job is being cancelled. */
+/**
+ * Returns whether the job is being cancelled.
+ * Called with job_mutex *not* held.
+ */
 bool job_is_cancelled(Job *job);
 
+/** Just like job_is_cancelled, but called between job_lock and job_unlock */
+bool job_is_cancelled_locked(Job *job);
+
 /**
  * Returns whether the job is scheduled for cancellation (at an
  * indefinite point).
+ * Called with job_mutex *not* held.
  */
 bool job_cancel_requested(Job *job);
 
-/** Returns whether the job is in a completed state. */
+/**
+ * Returns whether the job is in a completed state.
+ * Called with job_mutex *not* held.
+ */
 bool job_is_completed(Job *job);
 
-/** Returns whether the job is ready to be completed. */
+/** Same as job_is_completed(), but assumes job_lock is held. */
+bool job_is_completed_locked(Job *job);
+
+/**
+ * Returns whether the job is ready to be completed.
+ * Called with job_mutex *not* held.
+ */
 bool job_is_ready(Job *job);
 
+/** Same as job_is_ready(), but assumes job_lock is held. */
+bool job_is_ready_locked(Job *job);
+
 /**
  * Request @job to pause at the next pause point. Must be paired with
  * job_resume(). If the job is supposed to be resumed by user action, call
diff --git a/job.c b/job.c
index d8c13ac0d1..6f1f529dc1 100644
--- a/job.c
+++ b/job.c
@@ -222,19 +222,32 @@ const char *job_type_str(const Job *job)
     return JobType_str(job_type(job));
 }
 
-bool job_is_cancelled(Job *job)
+bool job_is_cancelled_locked(Job *job)
 {
     /* force_cancel may be true only if cancelled is true, too */
     assert(job->cancelled || !job->force_cancel);
     return job->force_cancel;
 }
 
-bool job_cancel_requested(Job *job)
+bool job_is_cancelled(Job *job)
+{
+    JOB_LOCK_GUARD();
+    return job_is_cancelled_locked(job);
+}
+
+/* Called with job_mutex held. */
+static bool job_cancel_requested_locked(Job *job)
 {
     return job->cancelled;
 }
 
-bool job_is_ready(Job *job)
+bool job_cancel_requested(Job *job)
+{
+    JOB_LOCK_GUARD();
+    return job_cancel_requested_locked(job);
+}
+
+bool job_is_ready_locked(Job *job)
 {
     switch (job->status) {
     case JOB_STATUS_UNDEFINED:
@@ -256,7 +269,13 @@ bool job_is_ready(Job *job)
     return false;
 }
 
-bool job_is_completed(Job *job)
+bool job_is_ready(Job *job)
+{
+    JOB_LOCK_GUARD();
+    return job_is_ready_locked(job);
+}
+
+bool job_is_completed_locked(Job *job)
 {
     switch (job->status) {
     case JOB_STATUS_UNDEFINED:
@@ -278,6 +297,12 @@ bool job_is_completed(Job *job)
     return false;
 }
 
+bool job_is_completed(Job *job)
+{
+    JOB_LOCK_GUARD();
+    return job_is_completed_locked(job);
+}
+
 static bool job_started(Job *job)
 {
     return job->co;
@@ -507,7 +532,8 @@ static void coroutine_fn job_do_yield(Job *job, uint64_t ns)
     assert(job->busy);
 }
 
-void coroutine_fn job_pause_point(Job *job)
+/* Called with job_mutex held, but releases it temporarly. */
+static void coroutine_fn job_pause_point_locked(Job *job)
 {
     assert(job && job_started(job));
 
@@ -538,6 +564,12 @@ void coroutine_fn job_pause_point(Job *job)
     }
 }
 
+void coroutine_fn job_pause_point(Job *job)
+{
+    JOB_LOCK_GUARD();
+    job_pause_point_locked(job);
+}
+
 void job_yield(Job *job)
 {
     assert(job->busy);
@@ -946,11 +978,15 @@ static void job_completed(Job *job)
     }
 }
 
-/** Useful only as a type shim for aio_bh_schedule_oneshot. */
+/**
+ * Useful only as a type shim for aio_bh_schedule_oneshot.
+ * Called with job_mutex *not* held.
+ */
 static void job_exit(void *opaque)
 {
     Job *job = (Job *)opaque;
     AioContext *ctx;
+    JOB_LOCK_GUARD();
 
     job_ref(job);
     aio_context_acquire(job->aio_context);
-- 
2.31.1

Re: [PATCH v5 07/20] job.h: add _locked duplicates for job API functions called with and without job_mutex

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 477 bytes --]

On Tue, Feb 08, 2022 at 09:35:00AM -0500, Emanuele Giuseppe Esposito wrote:
>  static void job_exit(void *opaque)
>  {
>      Job *job = (Job *)opaque;
>      AioContext *ctx;
> +    JOB_LOCK_GUARD();
>  
>      job_ref(job);
>      aio_context_acquire(job->aio_context);

The previous patch said:

  We don't want this, as job_lock must be taken inside the AioContext
  lock, and taking it outside would cause deadlocks.

Therefore this looks like a deadlock.

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Re: [PATCH v5 07/20] job.h: add _locked duplicates for job API functions called with and without job_mutex

[Emanuele Giuseppe Esposito]

On 17/02/2022 15:20, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:35:00AM -0500, Emanuele Giuseppe Esposito wrote:
>>  static void job_exit(void *opaque)
>>  {
>>      Job *job = (Job *)opaque;
>>      AioContext *ctx;
>> +    JOB_LOCK_GUARD();
>>  
>>      job_ref(job);
>>      aio_context_acquire(job->aio_context);
> 
> The previous patch said:
> 
>   We don't want this, as job_lock must be taken inside the AioContext
>   lock, and taking it outside would cause deadlocks.

This was misleading (and thus removed). You have to remember that at
this point JOB_LOCK_GUARD is nop.
I will add this to the commit message too.

> 
> Therefore this looks like a deadlock.
> 

[PATCH v5 08/20] jobs: protect jobs with job_lock/unlock

[Emanuele Giuseppe Esposito]

Introduce the job locking mechanism through the whole job API,
following the comments  in job.h and requirements of job-monitor
(like the functions in job-qmp.c, assume lock is held) and
job-driver (like in mirror.c and all other JobDriver, lock is not held).

Use the _locked helpers introduced before to differentiate
between functions called with and without job_mutex.
This only applies to function that are called under both
cases, all the others will be renamed later.

job_{lock/unlock} is independent from real_job_{lock/unlock}.

Note: at this stage, job_{lock/unlock} and job lock guard macros
are *nop*.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block.c             |  18 ++++---
 block/replication.c |   8 ++-
 blockdev.c          |  17 ++++--
 blockjob.c          |  62 +++++++++++++++-------
 job-qmp.c           |   2 +
 job.c               | 123 +++++++++++++++++++++++++++++++-------------
 monitor/qmp-cmds.c  |   6 ++-
 qemu-img.c          |  41 +++++++++------
 8 files changed, 191 insertions(+), 86 deletions(-)

diff --git a/block.c b/block.c
index 506c2f778d..33fe969fd9 100644
--- a/block.c
+++ b/block.c
@@ -4968,7 +4968,9 @@ static void bdrv_close(BlockDriverState *bs)
 
 void bdrv_close_all(void)
 {
-    assert(job_next(NULL) == NULL);
+    WITH_JOB_LOCK_GUARD() {
+        assert(job_next(NULL) == NULL);
+    }
     assert(qemu_in_main_thread());
 
     /* Drop references from requests still in flight, such as canceled block
@@ -6145,13 +6147,15 @@ XDbgBlockGraph *bdrv_get_xdbg_block_graph(Error **errp)
         }
     }
 
-    for (job = block_job_next(NULL); job; job = block_job_next(job)) {
-        GSList *el;
+    WITH_JOB_LOCK_GUARD() {
+        for (job = block_job_next(NULL); job; job = block_job_next(job)) {
+            GSList *el;
 
-        xdbg_graph_add_node(gr, job, X_DBG_BLOCK_GRAPH_NODE_TYPE_BLOCK_JOB,
-                           job->job.id);
-        for (el = job->nodes; el; el = el->next) {
-            xdbg_graph_add_edge(gr, job, (BdrvChild *)el->data);
+            xdbg_graph_add_node(gr, job, X_DBG_BLOCK_GRAPH_NODE_TYPE_BLOCK_JOB,
+                                job->job.id);
+            for (el = job->nodes; el; el = el->next) {
+                xdbg_graph_add_edge(gr, job, (BdrvChild *)el->data);
+            }
         }
     }
 
diff --git a/block/replication.c b/block/replication.c
index 55c8f894aa..a03b28726e 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -149,7 +149,9 @@ static void replication_close(BlockDriverState *bs)
     if (s->stage == BLOCK_REPLICATION_FAILOVER) {
         commit_job = &s->commit_job->job;
         assert(commit_job->aio_context == qemu_get_current_aio_context());
-        job_cancel_sync(commit_job, false);
+        WITH_JOB_LOCK_GUARD() {
+            job_cancel_sync(commit_job, false);
+        }
     }
 
     if (s->mode == REPLICATION_MODE_SECONDARY) {
@@ -726,7 +728,9 @@ static void replication_stop(ReplicationState *rs, bool failover, Error **errp)
          * disk, secondary disk in backup_job_completed().
          */
         if (s->backup_job) {
-            job_cancel_sync(&s->backup_job->job, true);
+            WITH_JOB_LOCK_GUARD() {
+                job_cancel_sync(&s->backup_job->job, true);
+            }
         }
 
         if (!failover) {
diff --git a/blockdev.c b/blockdev.c
index e315466914..c5fba4d157 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -150,6 +150,8 @@ void blockdev_mark_auto_del(BlockBackend *blk)
         return;
     }
 
+    JOB_LOCK_GUARD();
+
     for (job = block_job_next(NULL); job; job = block_job_next(job)) {
         if (block_job_has_bdrv(job, blk_bs(blk))) {
             AioContext *aio_context = job->job.aio_context;
@@ -1838,7 +1840,9 @@ static void drive_backup_abort(BlkActionState *common)
         aio_context = bdrv_get_aio_context(state->bs);
         aio_context_acquire(aio_context);
 
-        job_cancel_sync(&state->job->job, true);
+        WITH_JOB_LOCK_GUARD() {
+            job_cancel_sync(&state->job->job, true);
+        }
 
         aio_context_release(aio_context);
     }
@@ -1939,7 +1943,9 @@ static void blockdev_backup_abort(BlkActionState *common)
         aio_context = bdrv_get_aio_context(state->bs);
         aio_context_acquire(aio_context);
 
-        job_cancel_sync(&state->job->job, true);
+        WITH_JOB_LOCK_GUARD() {
+            job_cancel_sync(&state->job->job, true);
+        }
 
         aio_context_release(aio_context);
     }
@@ -2388,7 +2394,10 @@ exit:
     if (!has_props) {
         qapi_free_TransactionProperties(props);
     }
-    job_txn_unref(block_job_txn);
+
+    WITH_JOB_LOCK_GUARD() {
+        job_txn_unref(block_job_txn);
+    }
 }
 
 BlockDirtyBitmapSha256 *qmp_x_debug_block_dirty_bitmap_sha256(const char *node,
@@ -3711,6 +3720,8 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
     BlockJobInfoList *head = NULL, **tail = &head;
     BlockJob *job;
 
+    JOB_LOCK_GUARD();
+
     for (job = block_job_next(NULL); job; job = block_job_next(job)) {
         BlockJobInfo *value;
 
diff --git a/blockjob.c b/blockjob.c
index 98ce5cb1ed..5fb477fe26 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -102,7 +102,9 @@ static char *child_job_get_parent_desc(BdrvChild *c)
 static void child_job_drained_begin(BdrvChild *c)
 {
     BlockJob *job = c->opaque;
-    job_pause(&job->job);
+    WITH_JOB_LOCK_GUARD() {
+        job_pause(&job->job);
+    }
 }
 
 static bool child_job_drained_poll(BdrvChild *c)
@@ -114,8 +116,10 @@ static bool child_job_drained_poll(BdrvChild *c)
     /* An inactive or completed job doesn't have any pending requests. Jobs
      * with !job->busy are either already paused or have a pause point after
      * being reentered, so no job driver code will run before they pause. */
-    if (!job->busy || job_is_completed(job)) {
-        return false;
+    WITH_JOB_LOCK_GUARD() {
+        if (!job->busy || job_is_completed_locked(job)) {
+            return false;
+        }
     }
 
     /* Otherwise, assume that it isn't fully stopped yet, but allow the job to
@@ -130,7 +134,9 @@ static bool child_job_drained_poll(BdrvChild *c)
 static void child_job_drained_end(BdrvChild *c, int *drained_end_counter)
 {
     BlockJob *job = c->opaque;
-    job_resume(&job->job);
+    WITH_JOB_LOCK_GUARD() {
+        job_resume(&job->job);
+    }
 }
 
 static bool child_job_can_set_aio_ctx(BdrvChild *c, AioContext *ctx,
@@ -252,7 +258,13 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
 
 static void block_job_on_idle(Notifier *n, void *opaque)
 {
+    /*
+     * we can't kick with job_mutex held, but we also want
+     * to protect the notifier list.
+     */
+    job_unlock();
     aio_wait_kick();
+    job_lock();
 }
 
 bool block_job_is_internal(BlockJob *job)
@@ -292,7 +304,9 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
     job->speed = speed;
 
     if (drv->set_speed) {
+        job_unlock();
         drv->set_speed(job, speed);
+        job_lock();
     }
 
     if (speed && speed <= old_speed) {
@@ -334,7 +348,7 @@ BlockJobInfo *block_job_query(BlockJob *job, Error **errp)
     info->len       = progress_total;
     info->speed     = job->speed;
     info->io_status = job->iostatus;
-    info->ready     = job_is_ready(&job->job),
+    info->ready     = job_is_ready_locked(&job->job),
     info->status    = job->job.status;
     info->auto_finalize = job->job.auto_finalize;
     info->auto_dismiss  = job->job.auto_dismiss;
@@ -469,13 +483,15 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
     job->ready_notifier.notify = block_job_event_ready;
     job->idle_notifier.notify = block_job_on_idle;
 
-    notifier_list_add(&job->job.on_finalize_cancelled,
-                      &job->finalize_cancelled_notifier);
-    notifier_list_add(&job->job.on_finalize_completed,
-                      &job->finalize_completed_notifier);
-    notifier_list_add(&job->job.on_pending, &job->pending_notifier);
-    notifier_list_add(&job->job.on_ready, &job->ready_notifier);
-    notifier_list_add(&job->job.on_idle, &job->idle_notifier);
+    WITH_JOB_LOCK_GUARD() {
+        notifier_list_add(&job->job.on_finalize_cancelled,
+                          &job->finalize_cancelled_notifier);
+        notifier_list_add(&job->job.on_finalize_completed,
+                          &job->finalize_completed_notifier);
+        notifier_list_add(&job->job.on_pending, &job->pending_notifier);
+        notifier_list_add(&job->job.on_ready, &job->ready_notifier);
+        notifier_list_add(&job->job.on_idle, &job->idle_notifier);
+    }
 
     error_setg(&job->blocker, "block device is in use by block job: %s",
                job_type_str(&job->job));
@@ -487,7 +503,10 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
 
     bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
 
-    if (!block_job_set_speed(job, speed, errp)) {
+    WITH_JOB_LOCK_GUARD() {
+        ret = block_job_set_speed(job, speed, errp);
+    }
+    if (!ret) {
         goto fail;
     }
 
@@ -512,7 +531,9 @@ void block_job_user_resume(Job *job)
 {
     BlockJob *bjob = container_of(job, BlockJob, job);
     assert(qemu_in_main_thread());
-    block_job_iostatus_reset(bjob);
+    WITH_JOB_LOCK_GUARD() {
+        block_job_iostatus_reset(bjob);
+    }
 }
 
 BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
@@ -545,10 +566,15 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
                                         action);
     }
     if (action == BLOCK_ERROR_ACTION_STOP) {
-        if (!job->job.user_paused) {
-            job_pause(&job->job);
-            /* make the pause user visible, which will be resumed from QMP. */
-            job->job.user_paused = true;
+        WITH_JOB_LOCK_GUARD() {
+            if (!job->job.user_paused) {
+                job_pause(&job->job);
+                /*
+                 * make the pause user visible, which will be
+                 * resumed from QMP.
+                 */
+                job->job.user_paused = true;
+            }
         }
         block_job_iostatus_set_err(job, error);
     }
diff --git a/job-qmp.c b/job-qmp.c
index a6774aaaa5..06f970f6cf 100644
--- a/job-qmp.c
+++ b/job-qmp.c
@@ -171,6 +171,8 @@ JobInfoList *qmp_query_jobs(Error **errp)
     JobInfoList *head = NULL, **tail = &head;
     Job *job;
 
+    JOB_LOCK_GUARD();
+
     for (job = job_next(NULL); job; job = job_next(job)) {
         JobInfo *value;
 
diff --git a/job.c b/job.c
index 6f1f529dc1..75f7c28147 100644
--- a/job.c
+++ b/job.c
@@ -347,6 +347,8 @@ void *job_create(const char *job_id, const JobDriver *driver, JobTxn *txn,
 {
     Job *job;
 
+    JOB_LOCK_GUARD();
+
     if (job_id) {
         if (flags & JOB_INTERNAL) {
             error_setg(errp, "Cannot specify job ID for internal job");
@@ -421,7 +423,9 @@ void job_unref(Job *job)
         assert(!job->txn);
 
         if (job->driver->free) {
+            job_unlock();
             job->driver->free(job);
+            job_lock();
         }
 
         QLIST_REMOVE(job, job_list);
@@ -508,6 +512,7 @@ void job_enter_cond(Job *job, bool(*fn)(Job *job))
 
 void job_enter(Job *job)
 {
+    JOB_LOCK_GUARD();
     job_enter_cond(job, NULL);
 }
 
@@ -526,7 +531,9 @@ static void coroutine_fn job_do_yield(Job *job, uint64_t ns)
     job->busy = false;
     job_event_idle(job);
     real_job_unlock();
+    job_unlock();
     qemu_coroutine_yield();
+    job_lock();
 
     /* Set by job_enter_cond() before re-entering the coroutine.  */
     assert(job->busy);
@@ -540,15 +547,17 @@ static void coroutine_fn job_pause_point_locked(Job *job)
     if (!job_should_pause(job)) {
         return;
     }
-    if (job_is_cancelled(job)) {
+    if (job_is_cancelled_locked(job)) {
         return;
     }
 
     if (job->driver->pause) {
+        job_unlock();
         job->driver->pause(job);
+        job_lock();
     }
 
-    if (job_should_pause(job) && !job_is_cancelled(job)) {
+    if (job_should_pause(job) && !job_is_cancelled_locked(job)) {
         JobStatus status = job->status;
         job_state_transition(job, status == JOB_STATUS_READY
                                   ? JOB_STATUS_STANDBY
@@ -560,7 +569,9 @@ static void coroutine_fn job_pause_point_locked(Job *job)
     }
 
     if (job->driver->resume) {
+        job_unlock();
         job->driver->resume(job);
+        job_lock();
     }
 }
 
@@ -572,10 +583,11 @@ void coroutine_fn job_pause_point(Job *job)
 
 void job_yield(Job *job)
 {
+    JOB_LOCK_GUARD();
     assert(job->busy);
 
     /* Check cancellation *before* setting busy = false, too!  */
-    if (job_is_cancelled(job)) {
+    if (job_is_cancelled_locked(job)) {
         return;
     }
 
@@ -583,15 +595,16 @@ void job_yield(Job *job)
         job_do_yield(job, -1);
     }
 
-    job_pause_point(job);
+    job_pause_point_locked(job);
 }
 
 void coroutine_fn job_sleep_ns(Job *job, int64_t ns)
 {
+    JOB_LOCK_GUARD();
     assert(job->busy);
 
     /* Check cancellation *before* setting busy = false, too!  */
-    if (job_is_cancelled(job)) {
+    if (job_is_cancelled_locked(job)) {
         return;
     }
 
@@ -599,10 +612,10 @@ void coroutine_fn job_sleep_ns(Job *job, int64_t ns)
         job_do_yield(job, qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + ns);
     }
 
-    job_pause_point(job);
+    job_pause_point_locked(job);
 }
 
-/* Assumes the block_job_mutex is held */
+/* Assumes the job_mutex is held */
 static bool job_timer_not_pending(Job *job)
 {
     return !timer_pending(&job->sleep_timer);
@@ -612,7 +625,7 @@ void job_pause(Job *job)
 {
     job->pause_count++;
     if (!job->paused) {
-        job_enter(job);
+        job_enter_cond(job, NULL);
     }
 }
 
@@ -658,7 +671,9 @@ void job_user_resume(Job *job, Error **errp)
         return;
     }
     if (job->driver->user_resume) {
+        job_unlock();
         job->driver->user_resume(job);
+        job_lock();
     }
     job->user_paused = false;
     job_resume(job);
@@ -692,6 +707,7 @@ void job_dismiss(Job **jobptr, Error **errp)
 
 void job_early_fail(Job *job)
 {
+    JOB_LOCK_GUARD();
     assert(job->status == JOB_STATUS_CREATED);
     job_do_dismiss(job);
 }
@@ -706,7 +722,7 @@ static void job_conclude(Job *job)
 
 static void job_update_rc(Job *job)
 {
-    if (!job->ret && job_is_cancelled(job)) {
+    if (!job->ret && job_is_cancelled_locked(job)) {
         job->ret = -ECANCELED;
     }
     if (job->ret) {
@@ -722,7 +738,9 @@ static void job_commit(Job *job)
     assert(!job->ret);
     assert(qemu_in_main_thread());
     if (job->driver->commit) {
+        job_unlock();
         job->driver->commit(job);
+        job_lock();
     }
 }
 
@@ -731,7 +749,9 @@ static void job_abort(Job *job)
     assert(job->ret);
     assert(qemu_in_main_thread());
     if (job->driver->abort) {
+        job_unlock();
         job->driver->abort(job);
+        job_lock();
     }
 }
 
@@ -739,15 +759,18 @@ static void job_clean(Job *job)
 {
     assert(qemu_in_main_thread());
     if (job->driver->clean) {
+        job_unlock();
         job->driver->clean(job);
+        job_lock();
     }
 }
 
 static int job_finalize_single(Job *job)
 {
+    int job_ret;
     AioContext *ctx = job->aio_context;
 
-    assert(job_is_completed(job));
+    assert(job_is_completed_locked(job));
 
     /* Ensure abort is called for late-transactional failures */
     job_update_rc(job);
@@ -764,12 +787,15 @@ static int job_finalize_single(Job *job)
     aio_context_release(ctx);
 
     if (job->cb) {
-        job->cb(job->opaque, job->ret);
+        job_ret = job->ret;
+        job_unlock();
+        job->cb(job->opaque, job_ret);
+        job_lock();
     }
 
     /* Emit events only if we actually started */
     if (job_started(job)) {
-        if (job_is_cancelled(job)) {
+        if (job_is_cancelled_locked(job)) {
             job_event_cancelled(job);
         } else {
             job_event_completed(job);
@@ -785,7 +811,9 @@ static void job_cancel_async(Job *job, bool force)
 {
     assert(qemu_in_main_thread());
     if (job->driver->cancel) {
+        job_unlock();
         force = job->driver->cancel(job, force);
+        job_lock();
     } else {
         /* No .cancel() means the job will behave as if force-cancelled */
         force = true;
@@ -794,7 +822,9 @@ static void job_cancel_async(Job *job, bool force)
     if (job->user_paused) {
         /* Do not call job_enter here, the caller will handle it.  */
         if (job->driver->user_resume) {
+            job_unlock();
             job->driver->user_resume(job);
+            job_lock();
         }
         job->user_paused = false;
         assert(job->pause_count > 0);
@@ -863,8 +893,8 @@ static void job_completed_txn_abort(Job *job)
          */
         ctx = other_job->aio_context;
         aio_context_acquire(ctx);
-        if (!job_is_completed(other_job)) {
-            assert(job_cancel_requested(other_job));
+        if (!job_is_completed_locked(other_job)) {
+            assert(job_cancel_requested_locked(other_job));
             job_finish_sync(other_job, NULL, NULL);
         }
         aio_context_release(ctx);
@@ -883,13 +913,17 @@ static void job_completed_txn_abort(Job *job)
 
 static int job_prepare(Job *job)
 {
+    int ret;
     AioContext *ctx = job->aio_context;
     assert(qemu_in_main_thread());
 
     if (job->ret == 0 && job->driver->prepare) {
+        job_unlock();
         aio_context_acquire(ctx);
-        job->ret = job->driver->prepare(job);
+        ret = job->driver->prepare(job);
         aio_context_release(ctx);
+        job_lock();
+        job->ret = ret;
         job_update_rc(job);
     }
 
@@ -935,6 +969,7 @@ static int job_transition_to_pending(Job *job)
 
 void job_transition_to_ready(Job *job)
 {
+    JOB_LOCK_GUARD();
     job_state_transition(job, JOB_STATUS_READY);
     job_event_ready(job);
 }
@@ -951,7 +986,7 @@ static void job_completed_txn_success(Job *job)
      * txn.
      */
     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
-        if (!job_is_completed(other_job)) {
+        if (!job_is_completed_locked(other_job)) {
             return;
         }
         assert(other_job->ret == 0);
@@ -967,7 +1002,7 @@ static void job_completed_txn_success(Job *job)
 
 static void job_completed(Job *job)
 {
-    assert(job && job->txn && !job_is_completed(job));
+    assert(job && job->txn && !job_is_completed_locked(job));
 
     job_update_rc(job);
     trace_job_completed(job, job->ret);
@@ -1018,25 +1053,33 @@ static void job_exit(void *opaque)
 static void coroutine_fn job_co_entry(void *opaque)
 {
     Job *job = opaque;
+    int ret;
 
     assert(job && job->driver && job->driver->run);
-    assert(job->aio_context == qemu_get_current_aio_context());
-    job_pause_point(job);
-    job->ret = job->driver->run(job, &job->err);
-    job->deferred_to_main_loop = true;
-    job->busy = true;
+    WITH_JOB_LOCK_GUARD() {
+        assert(job->aio_context == qemu_get_current_aio_context());
+        job_pause_point_locked(job);
+    }
+    ret = job->driver->run(job, &job->err);
+    WITH_JOB_LOCK_GUARD() {
+        job->ret = ret;
+        job->deferred_to_main_loop = true;
+        job->busy = true;
+    }
     aio_bh_schedule_oneshot(qemu_get_aio_context(), job_exit, job);
 }
 
 void job_start(Job *job)
 {
-    assert(job && !job_started(job) && job->paused &&
-           job->driver && job->driver->run);
-    job->co = qemu_coroutine_create(job_co_entry, job);
-    job->pause_count--;
-    job->busy = true;
-    job->paused = false;
-    job_state_transition(job, JOB_STATUS_RUNNING);
+    WITH_JOB_LOCK_GUARD() {
+        assert(job && !job_started(job) && job->paused &&
+            job->driver && job->driver->run);
+        job->co = qemu_coroutine_create(job_co_entry, job);
+        job->pause_count--;
+        job->busy = true;
+        job->paused = false;
+        job_state_transition(job, JOB_STATUS_RUNNING);
+    }
     aio_co_enter(job->aio_context, job->co);
 }
 
@@ -1054,17 +1097,17 @@ void job_cancel(Job *job, bool force)
          * job_cancel_async() ignores soft-cancel requests for jobs
          * that are already done (i.e. deferred to the main loop).  We
          * have to check again whether the job is really cancelled.
-         * (job_cancel_requested() and job_is_cancelled() are equivalent
-         * here, because job_cancel_async() will make soft-cancel
-         * requests no-ops when deferred_to_main_loop is true.  We
-         * choose to call job_is_cancelled() to show that we invoke
+         * (job_cancel_requested_locked() and job_is_cancelled_locked()
+         * are equivalent here, because job_cancel_async() will
+         * make soft-cancel requests no-ops when deferred_to_main_loop is true.
+         * We choose to call job_is_cancelled_locked() to show that we invoke
          * job_completed_txn_abort() only for force-cancelled jobs.)
          */
-        if (job_is_cancelled(job)) {
+        if (job_is_cancelled_locked(job)) {
             job_completed_txn_abort(job);
         }
     } else {
-        job_enter(job);
+        job_enter_cond(job, NULL);
     }
 }
 
@@ -1106,6 +1149,7 @@ void job_cancel_sync_all(void)
     Job *job;
     AioContext *aio_context;
 
+    JOB_LOCK_GUARD();
     while ((job = job_next(NULL))) {
         aio_context = job->aio_context;
         aio_context_acquire(aio_context);
@@ -1127,13 +1171,15 @@ void job_complete(Job *job, Error **errp)
     if (job_apply_verb(job, JOB_VERB_COMPLETE, errp)) {
         return;
     }
-    if (job_cancel_requested(job) || !job->driver->complete) {
+    if (job_cancel_requested_locked(job) || !job->driver->complete) {
         error_setg(errp, "The active block job '%s' cannot be completed",
                    job->id);
         return;
     }
 
+    job_unlock();
     job->driver->complete(job, errp);
+    job_lock();
 }
 
 int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp)
@@ -1152,10 +1198,13 @@ int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp)
         return -EBUSY;
     }
 
+    job_unlock();
     AIO_WAIT_WHILE(job->aio_context,
                    (job_enter(job), !job_is_completed(job)));
+    job_lock();
 
-    ret = (job_is_cancelled(job) && job->ret == 0) ? -ECANCELED : job->ret;
+    ret = (job_is_cancelled_locked(job) && job->ret == 0)
+          ? -ECANCELED : job->ret;
     job_unref(job);
     return ret;
 }
diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
index 206d9a8c7b..97a16efcdc 100644
--- a/monitor/qmp-cmds.c
+++ b/monitor/qmp-cmds.c
@@ -134,8 +134,10 @@ void qmp_cont(Error **errp)
         blk_iostatus_reset(blk);
     }
 
-    for (job = block_job_next(NULL); job; job = block_job_next(job)) {
-        block_job_iostatus_reset(job);
+    WITH_JOB_LOCK_GUARD() {
+        for (job = block_job_next(NULL); job; job = block_job_next(job)) {
+            block_job_iostatus_reset(job);
+        }
     }
 
     /* Continuing after completed migration. Images have been inactivated to
diff --git a/qemu-img.c b/qemu-img.c
index 6fe2466032..320d82b42a 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -906,25 +906,30 @@ static void run_block_job(BlockJob *job, Error **errp)
     int ret = 0;
 
     aio_context_acquire(aio_context);
-    job_ref(&job->job);
-    do {
-        float progress = 0.0f;
-        aio_poll(aio_context, true);
+    WITH_JOB_LOCK_GUARD() {
+        job_ref(&job->job);
+        do {
+            float progress = 0.0f;
+            job_unlock();
+            aio_poll(aio_context, true);
+
+            progress_get_snapshot(&job->job.progress, &progress_current,
+                                &progress_total);
+            if (progress_total) {
+                progress = (float)progress_current / progress_total * 100.f;
+            }
+            qemu_progress_print(progress, 0);
+            job_lock();
+        } while (!job_is_ready_locked(&job->job) &&
+                 !job_is_completed_locked(&job->job));
 
-        progress_get_snapshot(&job->job.progress, &progress_current,
-                              &progress_total);
-        if (progress_total) {
-            progress = (float)progress_current / progress_total * 100.f;
+        if (!job_is_completed_locked(&job->job)) {
+            ret = job_complete_sync(&job->job, errp);
+        } else {
+            ret = job->job.ret;
         }
-        qemu_progress_print(progress, 0);
-    } while (!job_is_ready(&job->job) && !job_is_completed(&job->job));
-
-    if (!job_is_completed(&job->job)) {
-        ret = job_complete_sync(&job->job, errp);
-    } else {
-        ret = job->job.ret;
+        job_unref(&job->job);
     }
-    job_unref(&job->job);
     aio_context_release(aio_context);
 
     /* publish completion progress only when success */
@@ -1077,7 +1082,9 @@ static int img_commit(int argc, char **argv)
         bdrv_ref(bs);
     }
 
-    job = block_job_get("commit");
+    WITH_JOB_LOCK_GUARD() {
+        job = block_job_get("commit");
+    }
     assert(job);
     run_block_job(job, &local_err);
     if (local_err) {
-- 
2.31.1

Re: [PATCH v5 08/20] jobs: protect jobs with job_lock/unlock

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 3136 bytes --]

On Tue, Feb 08, 2022 at 09:35:01AM -0500, Emanuele Giuseppe Esposito wrote:
> diff --git a/block/replication.c b/block/replication.c
> index 55c8f894aa..a03b28726e 100644
> --- a/block/replication.c
> +++ b/block/replication.c
> @@ -149,7 +149,9 @@ static void replication_close(BlockDriverState *bs)
>      if (s->stage == BLOCK_REPLICATION_FAILOVER) {
>          commit_job = &s->commit_job->job;
>          assert(commit_job->aio_context == qemu_get_current_aio_context());

Is it safe to access commit_job->aio_context outside job_mutex?

> @@ -1838,7 +1840,9 @@ static void drive_backup_abort(BlkActionState *common)
>          aio_context = bdrv_get_aio_context(state->bs);
>          aio_context_acquire(aio_context);
>  
> -        job_cancel_sync(&state->job->job, true);
> +        WITH_JOB_LOCK_GUARD() {
> +            job_cancel_sync(&state->job->job, true);
> +        }

Maybe job_cancel_sync() should take the lock internally since all
callers in this patch seem to need the lock?

I noticed this patch does not add WITH_JOB_LOCK_GUARD() to
tests/unit/test-blockjob.c:cancel_common(). Was that an oversight or is
there a reason why job_mutex is not needed around the job_cancel_sync()
call there?

> @@ -252,7 +258,13 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
>  
>  static void block_job_on_idle(Notifier *n, void *opaque)
>  {
> +    /*
> +     * we can't kick with job_mutex held, but we also want
> +     * to protect the notifier list.
> +     */
> +    job_unlock();
>      aio_wait_kick();
> +    job_lock();

I don't understand this. aio_wait_kick() looks safe to call with a mutex
held?

> @@ -292,7 +304,9 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
>      job->speed = speed;
>  
>      if (drv->set_speed) {
> +        job_unlock();
>          drv->set_speed(job, speed);
> +        job_lock();

What guarantees that job stays alive during drv->set_speed(job)? We
don't hold a ref here. Maybe the assumption is that
block_job_set_speed() only gets called from the main loop thread and
nothing else will modify the jobs list while we're in drv->set_speed()?

> @@ -545,10 +566,15 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
>                                          action);
>      }
>      if (action == BLOCK_ERROR_ACTION_STOP) {
> -        if (!job->job.user_paused) {
> -            job_pause(&job->job);
> -            /* make the pause user visible, which will be resumed from QMP. */
> -            job->job.user_paused = true;
> +        WITH_JOB_LOCK_GUARD() {
> +            if (!job->job.user_paused) {
> +                job_pause(&job->job);
> +                /*
> +                 * make the pause user visible, which will be
> +                 * resumed from QMP.
> +                 */
> +                job->job.user_paused = true;
> +            }
>          }
>          block_job_iostatus_set_err(job, error);

Does this need the lock? If not, why is block_job_iostatus_reset()
called with the hold?

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH v5 08/20] jobs: protect jobs with job_lock/unlock

[Emanuele Giuseppe Esposito]

On 17/02/2022 15:48, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:35:01AM -0500, Emanuele Giuseppe Esposito wrote:
>> diff --git a/block/replication.c b/block/replication.c
>> index 55c8f894aa..a03b28726e 100644
>> --- a/block/replication.c
>> +++ b/block/replication.c
>> @@ -149,7 +149,9 @@ static void replication_close(BlockDriverState *bs)
>>      if (s->stage == BLOCK_REPLICATION_FAILOVER) {
>>          commit_job = &s->commit_job->job;
>>          assert(commit_job->aio_context == qemu_get_current_aio_context());
> 
> Is it safe to access commit_job->aio_context outside job_mutex?

No, but it is currently not done. Patch 18 takes care of protecting
aio_context. Remember again that job lock API is still nop.
> 
>> @@ -1838,7 +1840,9 @@ static void drive_backup_abort(BlkActionState *common)
>>          aio_context = bdrv_get_aio_context(state->bs);
>>          aio_context_acquire(aio_context);
>>  
>> -        job_cancel_sync(&state->job->job, true);
>> +        WITH_JOB_LOCK_GUARD() {
>> +            job_cancel_sync(&state->job->job, true);
>> +        }
> 
> Maybe job_cancel_sync() should take the lock internally since all
> callers in this patch seem to need the lock?

The _locked version is useful because it is used when lock guards are
already present, and cover multiple operations. There are only 3 places
where a lock guard is added to cover job_cance_sync_locked. Is it worth
defining another additional function?


> 
> I noticed this patch does not add WITH_JOB_LOCK_GUARD() to
> tests/unit/test-blockjob.c:cancel_common(). Was that an oversight or is
> there a reason why job_mutex is not needed around the job_cancel_sync()
> call there?

No, locks in unit tests are added in patch 10 "jobs: protect jobs with
job_lock/unlock".

> 
>> @@ -252,7 +258,13 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
>>  
>>  static void block_job_on_idle(Notifier *n, void *opaque)
>>  {
>> +    /*
>> +     * we can't kick with job_mutex held, but we also want
>> +     * to protect the notifier list.
>> +     */
>> +    job_unlock();
>>      aio_wait_kick();
>> +    job_lock();
> 
> I don't understand this. aio_wait_kick() looks safe to call with a mutex
> held?
You are right. It should be safe.

> 
>> @@ -292,7 +304,9 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
>>      job->speed = speed;
>>  
>>      if (drv->set_speed) {
>> +        job_unlock();
>>          drv->set_speed(job, speed);
>> +        job_lock();
> 
> What guarantees that job stays alive during drv->set_speed(job)? We
> don't hold a ref here. Maybe the assumption is that
> block_job_set_speed() only gets called from the main loop thread and
> nothing else will modify the jobs list while we're in drv->set_speed()?

What guaranteed this before? I am not sure.

> 
>> @@ -545,10 +566,15 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
>>                                          action);
>>      }
>>      if (action == BLOCK_ERROR_ACTION_STOP) {
>> -        if (!job->job.user_paused) {
>> -            job_pause(&job->job);
>> -            /* make the pause user visible, which will be resumed from QMP. */
>> -            job->job.user_paused = true;
>> +        WITH_JOB_LOCK_GUARD() {
>> +            if (!job->job.user_paused) {
>> +                job_pause(&job->job);
>> +                /*
>> +                 * make the pause user visible, which will be
>> +                 * resumed from QMP.
>> +                 */
>> +                job->job.user_paused = true;
>> +            }
>>          }
>>          block_job_iostatus_set_err(job, error);
> 
> Does this need the lock? If not, why is block_job_iostatus_reset()
> called with the hold?
> 
block_job_iostatus_set_err does not touch any Job fields. On the other
hand block_job_iostatus_reset reads job.user_paused and job.pause_count.

Emanuele

Re: [PATCH v5 08/20] jobs: protect jobs with job_lock/unlock

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 4977 bytes --]

On Thu, Feb 24, 2022 at 01:45:48PM +0100, Emanuele Giuseppe Esposito wrote:
> 
> 
> On 17/02/2022 15:48, Stefan Hajnoczi wrote:
> > On Tue, Feb 08, 2022 at 09:35:01AM -0500, Emanuele Giuseppe Esposito wrote:
> >> diff --git a/block/replication.c b/block/replication.c
> >> index 55c8f894aa..a03b28726e 100644
> >> --- a/block/replication.c
> >> +++ b/block/replication.c
> >> @@ -149,7 +149,9 @@ static void replication_close(BlockDriverState *bs)
> >>      if (s->stage == BLOCK_REPLICATION_FAILOVER) {
> >>          commit_job = &s->commit_job->job;
> >>          assert(commit_job->aio_context == qemu_get_current_aio_context());
> > 
> > Is it safe to access commit_job->aio_context outside job_mutex?
> 
> No, but it is currently not done. Patch 18 takes care of protecting
> aio_context. Remember again that job lock API is still nop.
> > 
> >> @@ -1838,7 +1840,9 @@ static void drive_backup_abort(BlkActionState *common)
> >>          aio_context = bdrv_get_aio_context(state->bs);
> >>          aio_context_acquire(aio_context);
> >>  
> >> -        job_cancel_sync(&state->job->job, true);
> >> +        WITH_JOB_LOCK_GUARD() {
> >> +            job_cancel_sync(&state->job->job, true);
> >> +        }
> > 
> > Maybe job_cancel_sync() should take the lock internally since all
> > callers in this patch seem to need the lock?
> 
> The _locked version is useful because it is used when lock guards are
> already present, and cover multiple operations. There are only 3 places
> where a lock guard is added to cover job_cance_sync_locked. Is it worth
> defining another additional function?
> 
> 
> > 
> > I noticed this patch does not add WITH_JOB_LOCK_GUARD() to
> > tests/unit/test-blockjob.c:cancel_common(). Was that an oversight or is
> > there a reason why job_mutex is not needed around the job_cancel_sync()
> > call there?
> 
> No, locks in unit tests are added in patch 10 "jobs: protect jobs with
> job_lock/unlock".

I see, it's a question of how to split up the patches. When patches
leave the code in a state with broken invariants it becomes difficult to
review. I can't distinguish between actual bugs and temporary violations
that will be fixed in a later patch (unless they are clearly marked).

If you can structure patches so they are self-contained and don't leave
the broken invariants then that would make review easier, but in this
case it is tricky so I'll do the best I can to review it if you cannot
restructure the sequence of commits.

> > 
> >> @@ -252,7 +258,13 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
> >>  
> >>  static void block_job_on_idle(Notifier *n, void *opaque)
> >>  {
> >> +    /*
> >> +     * we can't kick with job_mutex held, but we also want
> >> +     * to protect the notifier list.
> >> +     */
> >> +    job_unlock();
> >>      aio_wait_kick();
> >> +    job_lock();
> > 
> > I don't understand this. aio_wait_kick() looks safe to call with a mutex
> > held?
> You are right. It should be safe.
> 
> > 
> >> @@ -292,7 +304,9 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
> >>      job->speed = speed;
> >>  
> >>      if (drv->set_speed) {
> >> +        job_unlock();
> >>          drv->set_speed(job, speed);
> >> +        job_lock();
> > 
> > What guarantees that job stays alive during drv->set_speed(job)? We
> > don't hold a ref here. Maybe the assumption is that
> > block_job_set_speed() only gets called from the main loop thread and
> > nothing else will modify the jobs list while we're in drv->set_speed()?
> 
> What guaranteed this before? I am not sure.

I guess the reason is the one I suggested. It should be documented in
the comments.

> 
> > 
> >> @@ -545,10 +566,15 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
> >>                                          action);
> >>      }
> >>      if (action == BLOCK_ERROR_ACTION_STOP) {
> >> -        if (!job->job.user_paused) {
> >> -            job_pause(&job->job);
> >> -            /* make the pause user visible, which will be resumed from QMP. */
> >> -            job->job.user_paused = true;
> >> +        WITH_JOB_LOCK_GUARD() {
> >> +            if (!job->job.user_paused) {
> >> +                job_pause(&job->job);
> >> +                /*
> >> +                 * make the pause user visible, which will be
> >> +                 * resumed from QMP.
> >> +                 */
> >> +                job->job.user_paused = true;
> >> +            }
> >>          }
> >>          block_job_iostatus_set_err(job, error);
> > 
> > Does this need the lock? If not, why is block_job_iostatus_reset()
> > called with the hold?
> > 
> block_job_iostatus_set_err does not touch any Job fields. On the other
> hand block_job_iostatus_reset reads job.user_paused and job.pause_count.

BlockJob->iostatus requires no locking?

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Re: [PATCH v5 08/20] jobs: protect jobs with job_lock/unlock

[Emanuele Giuseppe Esposito]

On 24/02/2022 17:48, Stefan Hajnoczi wrote:
> On Thu, Feb 24, 2022 at 01:45:48PM +0100, Emanuele Giuseppe Esposito wrote:
>>
>>
>> On 17/02/2022 15:48, Stefan Hajnoczi wrote:
>>> On Tue, Feb 08, 2022 at 09:35:01AM -0500, Emanuele Giuseppe Esposito wrote:
>>>> diff --git a/block/replication.c b/block/replication.c
>>>> index 55c8f894aa..a03b28726e 100644
>>>> --- a/block/replication.c
>>>> +++ b/block/replication.c
>>>> @@ -149,7 +149,9 @@ static void replication_close(BlockDriverState *bs)
>>>>      if (s->stage == BLOCK_REPLICATION_FAILOVER) {
>>>>          commit_job = &s->commit_job->job;
>>>>          assert(commit_job->aio_context == qemu_get_current_aio_context());
>>>
>>> Is it safe to access commit_job->aio_context outside job_mutex?
>>
>> No, but it is currently not done. Patch 18 takes care of protecting
>> aio_context. Remember again that job lock API is still nop.
>>>
>>>> @@ -1838,7 +1840,9 @@ static void drive_backup_abort(BlkActionState *common)
>>>>          aio_context = bdrv_get_aio_context(state->bs);
>>>>          aio_context_acquire(aio_context);
>>>>  
>>>> -        job_cancel_sync(&state->job->job, true);
>>>> +        WITH_JOB_LOCK_GUARD() {
>>>> +            job_cancel_sync(&state->job->job, true);
>>>> +        }
>>>
>>> Maybe job_cancel_sync() should take the lock internally since all
>>> callers in this patch seem to need the lock?
>>
>> The _locked version is useful because it is used when lock guards are
>> already present, and cover multiple operations. There are only 3 places
>> where a lock guard is added to cover job_cance_sync_locked. Is it worth
>> defining another additional function?
>>
>>
>>>
>>> I noticed this patch does not add WITH_JOB_LOCK_GUARD() to
>>> tests/unit/test-blockjob.c:cancel_common(). Was that an oversight or is
>>> there a reason why job_mutex is not needed around the job_cancel_sync()
>>> call there?
>>
>> No, locks in unit tests are added in patch 10 "jobs: protect jobs with
>> job_lock/unlock".
> 
> I see, it's a question of how to split up the patches. When patches
> leave the code in a state with broken invariants it becomes difficult to
> review. I can't distinguish between actual bugs and temporary violations
> that will be fixed in a later patch (unless they are clearly marked).
> 
> If you can structure patches so they are self-contained and don't leave
> the broken invariants then that would make review easier, but in this
> case it is tricky so I'll do the best I can to review it if you cannot
> restructure the sequence of commits.

Yes, the main problem is that ideally we want to add job lock and remove
Aiocontext lock. But together this can't happen, and just adding proper
locks will create a ton of deadlocks, because in order to maintain
invariants sometimes job lock is inside aiocontext lock, and some other
times the opposite happens.

The way it is done in this serie is:
1) create job_lock/unlock as nop
2) make sure the nop job_lock is protecting the Job fields
3) do all API renaming, accoring with the locking used above
4) enable job_lock (not nop anymore) and at the same time remove the
AioContext

If you want, a more up-to-date branch with your feedbacks applied so far
is here:
https://gitlab.com/eesposit/qemu/-/commits/dp_jobs_reviewed

> 
>>>
>>>> @@ -252,7 +258,13 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
>>>>  
>>>>  static void block_job_on_idle(Notifier *n, void *opaque)
>>>>  {
>>>> +    /*
>>>> +     * we can't kick with job_mutex held, but we also want
>>>> +     * to protect the notifier list.
>>>> +     */
>>>> +    job_unlock();
>>>>      aio_wait_kick();
>>>> +    job_lock();
>>>
>>> I don't understand this. aio_wait_kick() looks safe to call with a mutex
>>> held?
>> You are right. It should be safe.
>>
>>>
>>>> @@ -292,7 +304,9 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
>>>>      job->speed = speed;
>>>>  
>>>>      if (drv->set_speed) {
>>>> +        job_unlock();
>>>>          drv->set_speed(job, speed);
>>>> +        job_lock();
>>>
>>> What guarantees that job stays alive during drv->set_speed(job)? We
>>> don't hold a ref here. Maybe the assumption is that
>>> block_job_set_speed() only gets called from the main loop thread and
>>> nothing else will modify the jobs list while we're in drv->set_speed()?
>>
>> What guaranteed this before? I am not sure.
> 
> I guess the reason is the one I suggested. It should be documented in
> the comments.
> 
>>
>>>
>>>> @@ -545,10 +566,15 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
>>>>                                          action);
>>>>      }
>>>>      if (action == BLOCK_ERROR_ACTION_STOP) {
>>>> -        if (!job->job.user_paused) {
>>>> -            job_pause(&job->job);
>>>> -            /* make the pause user visible, which will be resumed from QMP. */
>>>> -            job->job.user_paused = true;
>>>> +        WITH_JOB_LOCK_GUARD() {
>>>> +            if (!job->job.user_paused) {
>>>> +                job_pause(&job->job);
>>>> +                /*
>>>> +                 * make the pause user visible, which will be
>>>> +                 * resumed from QMP.
>>>> +                 */
>>>> +                job->job.user_paused = true;
>>>> +            }
>>>>          }
>>>>          block_job_iostatus_set_err(job, error);
>>>
>>> Does this need the lock? If not, why is block_job_iostatus_reset()
>>> called with the hold?
>>>
>> block_job_iostatus_set_err does not touch any Job fields. On the other
>> hand block_job_iostatus_reset reads job.user_paused and job.pause_count.
> 
> BlockJob->iostatus requires no locking?
> 

[PATCH v5 09/20] jobs: add job lock in find_* functions

[Emanuele Giuseppe Esposito]

Both blockdev.c and job-qmp.c have TOC/TOU conditions, because
they first search for the job and then perform an action on it.
Therefore, we need to do the search + action under the same
job mutex critical section.

Note: at this stage, job_{lock/unlock} and job lock guard macros
are *nop*.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 blockdev.c | 14 +++++++++++++-
 job-qmp.c  | 13 ++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index c5fba4d157..08408cd44b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3311,7 +3311,10 @@ out:
     aio_context_release(aio_context);
 }
 
-/* Get a block job using its ID and acquire its AioContext */
+/*
+ * Get a block job using its ID and acquire its AioContext.
+ * Returns with job_lock held on success.
+ */
 static BlockJob *find_block_job(const char *id, AioContext **aio_context,
                                 Error **errp)
 {
@@ -3320,12 +3323,14 @@ static BlockJob *find_block_job(const char *id, AioContext **aio_context,
     assert(id != NULL);
 
     *aio_context = NULL;
+    job_lock();
 
     job = block_job_get(id);
 
     if (!job) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
                   "Block job '%s' not found", id);
+        job_unlock();
         return NULL;
     }
 
@@ -3346,6 +3351,7 @@ void qmp_block_job_set_speed(const char *device, int64_t speed, Error **errp)
 
     block_job_set_speed(job, speed, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_block_job_cancel(const char *device,
@@ -3372,6 +3378,7 @@ void qmp_block_job_cancel(const char *device,
     job_user_cancel(&job->job, force, errp);
 out:
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_block_job_pause(const char *device, Error **errp)
@@ -3386,6 +3393,7 @@ void qmp_block_job_pause(const char *device, Error **errp)
     trace_qmp_block_job_pause(job);
     job_user_pause(&job->job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_block_job_resume(const char *device, Error **errp)
@@ -3400,6 +3408,7 @@ void qmp_block_job_resume(const char *device, Error **errp)
     trace_qmp_block_job_resume(job);
     job_user_resume(&job->job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_block_job_complete(const char *device, Error **errp)
@@ -3414,6 +3423,7 @@ void qmp_block_job_complete(const char *device, Error **errp)
     trace_qmp_block_job_complete(job);
     job_complete(&job->job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_block_job_finalize(const char *id, Error **errp)
@@ -3437,6 +3447,7 @@ void qmp_block_job_finalize(const char *id, Error **errp)
     aio_context = block_job_get_aio_context(job);
     job_unref(&job->job);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_block_job_dismiss(const char *id, Error **errp)
@@ -3453,6 +3464,7 @@ void qmp_block_job_dismiss(const char *id, Error **errp)
     job = &bjob->job;
     job_dismiss(&job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_change_backing_file(const char *device,
diff --git a/job-qmp.c b/job-qmp.c
index 06f970f6cf..a08cd7dd36 100644
--- a/job-qmp.c
+++ b/job-qmp.c
@@ -29,16 +29,21 @@
 #include "qapi/error.h"
 #include "trace/trace-root.h"
 
-/* Get a job using its ID and acquire its AioContext */
+/*
+ * Get a block job using its ID and acquire its AioContext.
+ * Returns with job_lock held on success.
+ */
 static Job *find_job(const char *id, AioContext **aio_context, Error **errp)
 {
     Job *job;
 
     *aio_context = NULL;
+    job_lock();
 
     job = job_get(id);
     if (!job) {
         error_setg(errp, "Job not found");
+        job_unlock();
         return NULL;
     }
 
@@ -60,6 +65,7 @@ void qmp_job_cancel(const char *id, Error **errp)
     trace_qmp_job_cancel(job);
     job_user_cancel(job, true, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_job_pause(const char *id, Error **errp)
@@ -74,6 +80,7 @@ void qmp_job_pause(const char *id, Error **errp)
     trace_qmp_job_pause(job);
     job_user_pause(job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_job_resume(const char *id, Error **errp)
@@ -88,6 +95,7 @@ void qmp_job_resume(const char *id, Error **errp)
     trace_qmp_job_resume(job);
     job_user_resume(job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_job_complete(const char *id, Error **errp)
@@ -102,6 +110,7 @@ void qmp_job_complete(const char *id, Error **errp)
     trace_qmp_job_complete(job);
     job_complete(job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_job_finalize(const char *id, Error **errp)
@@ -125,6 +134,7 @@ void qmp_job_finalize(const char *id, Error **errp)
     aio_context = job->aio_context;
     job_unref(job);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 void qmp_job_dismiss(const char *id, Error **errp)
@@ -139,6 +149,7 @@ void qmp_job_dismiss(const char *id, Error **errp)
     trace_qmp_job_dismiss(job);
     job_dismiss(&job, errp);
     aio_context_release(aio_context);
+    job_unlock();
 }
 
 static JobInfo *job_query_single(Job *job, Error **errp)
-- 
2.31.1

Re: [PATCH v5 09/20] jobs: add job lock in find_* functions

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1039 bytes --]

On Tue, Feb 08, 2022 at 09:35:02AM -0500, Emanuele Giuseppe Esposito wrote:
> diff --git a/blockdev.c b/blockdev.c
> index c5fba4d157..08408cd44b 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3311,7 +3311,10 @@ out:
>      aio_context_release(aio_context);
>  }
>  
> -/* Get a block job using its ID and acquire its AioContext */
> +/*
> + * Get a block job using its ID and acquire its AioContext.
> + * Returns with job_lock held on success.

The caller needs to deal with unlocking anyway, so maybe ask the caller
to acquire the lock too? That would make the function simpler to reason
about.

> @@ -60,6 +65,7 @@ void qmp_job_cancel(const char *id, Error **errp)
>      trace_qmp_job_cancel(job);
>      job_user_cancel(job, true, errp);
>      aio_context_release(aio_context);
> +    job_unlock();
>  }

Is job_mutex -> AioContext lock ordering correct? I thought the
AioContext must be held before taking the job lock according to "jobs:
remove aiocontext locks since the functions are under BQL"?

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Re: [PATCH v5 09/20] jobs: add job lock in find_* functions

[Emanuele Giuseppe Esposito]

On 17/02/2022 16:00, Stefan Hajnoczi wrote:
> On Tue, Feb 08, 2022 at 09:35:02AM -0500, Emanuele Giuseppe Esposito wrote:
>> diff --git a/blockdev.c b/blockdev.c
>> index c5fba4d157..08408cd44b 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -3311,7 +3311,10 @@ out:
>>      aio_context_release(aio_context);
>>  }
>>  
>> -/* Get a block job using its ID and acquire its AioContext */
>> +/*
>> + * Get a block job using its ID and acquire its AioContext.
>> + * Returns with job_lock held on success.
> 
> The caller needs to deal with unlocking anyway, so maybe ask the caller
> to acquire the lock too? That would make the function simpler to reason
> about.

Those aiocontext locks there are going to be removed when job
lock/unlock are enabled, so it is useless to modify the logic now.
It makes sense to apply this logic with job_lock/unlock though.

> 
>> @@ -60,6 +65,7 @@ void qmp_job_cancel(const char *id, Error **errp)
>>      trace_qmp_job_cancel(job);
>>      job_user_cancel(job, true, errp);
>>      aio_context_release(aio_context);
>> +    job_unlock();
>>  }
> 
> Is job_mutex -> AioContext lock ordering correct? I thought the
> AioContext must be held before taking the job lock according to "jobs:
> remove aiocontext locks since the functions are under BQL"?
> 

I think you got it at this point, but anyways: job_lock is nop and when
it will be enabled, aio_context_acquire will go away in the same patch.

Thank you,
Emanuele

[PATCH v5 10/20] jobs: use job locks also in the unit tests

[Emanuele Giuseppe Esposito]

Add missing job synchronization in the unit tests, with
explicit locks.

Note: at this stage, job_{lock/unlock} and job lock guard macros
are *nop*.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 tests/unit/test-bdrv-drain.c     | 76 ++++++++++++++++---------
 tests/unit/test-block-iothread.c |  8 ++-
 tests/unit/test-blockjob-txn.c   | 32 +++++++----
 tests/unit/test-blockjob.c       | 96 ++++++++++++++++++++++++--------
 4 files changed, 148 insertions(+), 64 deletions(-)

diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index 36be84ae55..181458eecb 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -943,61 +943,83 @@ static void test_blockjob_common_drain_node(enum drain_type drain_type,
         }
     }
 
-    g_assert_cmpint(job->job.pause_count, ==, 0);
-    g_assert_false(job->job.paused);
-    g_assert_true(tjob->running);
-    g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
+    WITH_JOB_LOCK_GUARD() {
+        g_assert_cmpint(job->job.pause_count, ==, 0);
+        g_assert_false(job->job.paused);
+        g_assert_true(tjob->running);
+        g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
+    }
 
     do_drain_begin_unlocked(drain_type, drain_bs);
 
-    if (drain_type == BDRV_DRAIN_ALL) {
-        /* bdrv_drain_all() drains both src and target */
-        g_assert_cmpint(job->job.pause_count, ==, 2);
-    } else {
-        g_assert_cmpint(job->job.pause_count, ==, 1);
+    WITH_JOB_LOCK_GUARD() {
+        if (drain_type == BDRV_DRAIN_ALL) {
+            /* bdrv_drain_all() drains both src and target */
+            g_assert_cmpint(job->job.pause_count, ==, 2);
+        } else {
+            g_assert_cmpint(job->job.pause_count, ==, 1);
+        }
+        g_assert_true(job->job.paused);
+        g_assert_false(job->job.busy); /* The job is paused */
     }
-    g_assert_true(job->job.paused);
-    g_assert_false(job->job.busy); /* The job is paused */
 
     do_drain_end_unlocked(drain_type, drain_bs);
 
     if (use_iothread) {
-        /* paused is reset in the I/O thread, wait for it */
+        /*
+         * Here we are waiting for the paused status to change,
+         * so don't bother protecting the read every time.
+         *
+         * paused is reset in the I/O thread, wait for it
+         */
         while (job->job.paused) {
             aio_poll(qemu_get_aio_context(), false);
         }
     }
 
-    g_assert_cmpint(job->job.pause_count, ==, 0);
-    g_assert_false(job->job.paused);
-    g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
+    WITH_JOB_LOCK_GUARD() {
+        g_assert_cmpint(job->job.pause_count, ==, 0);
+        g_assert_false(job->job.paused);
+        g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
+    }
 
     do_drain_begin_unlocked(drain_type, target);
 
-    if (drain_type == BDRV_DRAIN_ALL) {
-        /* bdrv_drain_all() drains both src and target */
-        g_assert_cmpint(job->job.pause_count, ==, 2);
-    } else {
-        g_assert_cmpint(job->job.pause_count, ==, 1);
+    WITH_JOB_LOCK_GUARD() {
+        if (drain_type == BDRV_DRAIN_ALL) {
+            /* bdrv_drain_all() drains both src and target */
+            g_assert_cmpint(job->job.pause_count, ==, 2);
+        } else {
+            g_assert_cmpint(job->job.pause_count, ==, 1);
+        }
+        g_assert_true(job->job.paused);
+        g_assert_false(job->job.busy); /* The job is paused */
     }
-    g_assert_true(job->job.paused);
-    g_assert_false(job->job.busy); /* The job is paused */
 
     do_drain_end_unlocked(drain_type, target);
 
     if (use_iothread) {
-        /* paused is reset in the I/O thread, wait for it */
+        /*
+         * Here we are waiting for the paused status to change,
+         * so don't bother protecting the read every time.
+         *
+         * paused is reset in the I/O thread, wait for it
+         */
         while (job->job.paused) {
             aio_poll(qemu_get_aio_context(), false);
         }
     }
 
-    g_assert_cmpint(job->job.pause_count, ==, 0);
-    g_assert_false(job->job.paused);
-    g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
+    WITH_JOB_LOCK_GUARD() {
+        g_assert_cmpint(job->job.pause_count, ==, 0);
+        g_assert_false(job->job.paused);
+        g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
+    }
 
     aio_context_acquire(ctx);
-    ret = job_complete_sync(&job->job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        ret = job_complete_sync(&job->job, &error_abort);
+    }
     g_assert_cmpint(ret, ==, (result == TEST_JOB_SUCCESS ? 0 : -EIO));
 
     if (use_iothread) {
diff --git a/tests/unit/test-block-iothread.c b/tests/unit/test-block-iothread.c
index 94718c9319..9866262f79 100644
--- a/tests/unit/test-block-iothread.c
+++ b/tests/unit/test-block-iothread.c
@@ -456,7 +456,9 @@ static void test_attach_blockjob(void)
     }
 
     aio_context_acquire(ctx);
-    job_complete_sync(&tjob->common.job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_complete_sync(&tjob->common.job, &error_abort);
+    }
     blk_set_aio_context(blk, qemu_get_aio_context(), &error_abort);
     aio_context_release(ctx);
 
@@ -630,7 +632,9 @@ static void test_propagate_mirror(void)
                  BLOCKDEV_ON_ERROR_REPORT, BLOCKDEV_ON_ERROR_REPORT,
                  false, "filter_node", MIRROR_COPY_MODE_BACKGROUND,
                  &error_abort);
-    job = job_get("job0");
+    WITH_JOB_LOCK_GUARD() {
+        job = job_get("job0");
+    }
     filter = bdrv_find_node("filter_node");
 
     /* Change the AioContext of src */
diff --git a/tests/unit/test-blockjob-txn.c b/tests/unit/test-blockjob-txn.c
index c69028b450..0355e54001 100644
--- a/tests/unit/test-blockjob-txn.c
+++ b/tests/unit/test-blockjob-txn.c
@@ -116,8 +116,10 @@ static void test_single_job(int expected)
     job = test_block_job_start(1, true, expected, &result, txn);
     job_start(&job->job);
 
-    if (expected == -ECANCELED) {
-        job_cancel(&job->job, false);
+    WITH_JOB_LOCK_GUARD() {
+        if (expected == -ECANCELED) {
+            job_cancel(&job->job, false);
+        }
     }
 
     while (result == -EINPROGRESS) {
@@ -125,7 +127,9 @@ static void test_single_job(int expected)
     }
     g_assert_cmpint(result, ==, expected);
 
-    job_txn_unref(txn);
+    WITH_JOB_LOCK_GUARD() {
+        job_txn_unref(txn);
+    }
 }
 
 static void test_single_job_success(void)
@@ -160,13 +164,15 @@ static void test_pair_jobs(int expected1, int expected2)
     /* Release our reference now to trigger as many nice
      * use-after-free bugs as possible.
      */
-    job_txn_unref(txn);
+    WITH_JOB_LOCK_GUARD() {
+        job_txn_unref(txn);
 
-    if (expected1 == -ECANCELED) {
-        job_cancel(&job1->job, false);
-    }
-    if (expected2 == -ECANCELED) {
-        job_cancel(&job2->job, false);
+        if (expected1 == -ECANCELED) {
+            job_cancel(&job1->job, false);
+        }
+        if (expected2 == -ECANCELED) {
+            job_cancel(&job2->job, false);
+        }
     }
 
     while (result1 == -EINPROGRESS || result2 == -EINPROGRESS) {
@@ -219,7 +225,9 @@ static void test_pair_jobs_fail_cancel_race(void)
     job_start(&job1->job);
     job_start(&job2->job);
 
-    job_cancel(&job1->job, false);
+    WITH_JOB_LOCK_GUARD() {
+        job_cancel(&job1->job, false);
+    }
 
     /* Now make job2 finish before the main loop kicks jobs.  This simulates
      * the race between a pending kick and another job completing.
@@ -234,7 +242,9 @@ static void test_pair_jobs_fail_cancel_race(void)
     g_assert_cmpint(result1, ==, -ECANCELED);
     g_assert_cmpint(result2, ==, -ECANCELED);
 
-    job_txn_unref(txn);
+    WITH_JOB_LOCK_GUARD() {
+        job_txn_unref(txn);
+    }
 }
 
 int main(int argc, char **argv)
diff --git a/tests/unit/test-blockjob.c b/tests/unit/test-blockjob.c
index 4c9e1bf1e5..ab7958dad5 100644
--- a/tests/unit/test-blockjob.c
+++ b/tests/unit/test-blockjob.c
@@ -211,8 +211,11 @@ static CancelJob *create_common(Job **pjob)
     bjob = mk_job(blk, "Steve", &test_cancel_driver, true,
                   JOB_MANUAL_FINALIZE | JOB_MANUAL_DISMISS);
     job = &bjob->job;
-    job_ref(job);
-    assert(job->status == JOB_STATUS_CREATED);
+    WITH_JOB_LOCK_GUARD() {
+        job_ref(job);
+        assert(job->status == JOB_STATUS_CREATED);
+    }
+
     s = container_of(bjob, CancelJob, common);
     s->blk = blk;
 
@@ -230,13 +233,15 @@ static void cancel_common(CancelJob *s)
     ctx = job->job.aio_context;
     aio_context_acquire(ctx);
 
-    job_cancel_sync(&job->job, true);
-    if (sts != JOB_STATUS_CREATED && sts != JOB_STATUS_CONCLUDED) {
-        Job *dummy = &job->job;
-        job_dismiss(&dummy, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_cancel_sync(&job->job, true);
+        if (sts != JOB_STATUS_CREATED && sts != JOB_STATUS_CONCLUDED) {
+            Job *dummy = &job->job;
+            job_dismiss(&dummy, &error_abort);
+        }
+        assert(job->job.status == JOB_STATUS_NULL);
+        job_unref(&job->job);
     }
-    assert(job->job.status == JOB_STATUS_NULL);
-    job_unref(&job->job);
     destroy_blk(blk);
 
     aio_context_release(ctx);
@@ -251,6 +256,10 @@ static void test_cancel_created(void)
     cancel_common(s);
 }
 
+/*
+ * This test always runs in the main loop, so there is no
+ * need to protect job->status.
+ */
 static void test_cancel_running(void)
 {
     Job *job;
@@ -264,6 +273,10 @@ static void test_cancel_running(void)
     cancel_common(s);
 }
 
+/*
+ * This test always runs in the main loop, so there is no
+ * need to protect job->status.
+ */
 static void test_cancel_paused(void)
 {
     Job *job;
@@ -274,13 +287,19 @@ static void test_cancel_paused(void)
     job_start(job);
     assert(job->status == JOB_STATUS_RUNNING);
 
-    job_user_pause(job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_user_pause(job, &error_abort);
+    }
     job_enter(job);
     assert(job->status == JOB_STATUS_PAUSED);
 
     cancel_common(s);
 }
 
+/*
+ * This test always runs in the main loop, so there is no
+ * need to protect job->status.
+ */
 static void test_cancel_ready(void)
 {
     Job *job;
@@ -298,6 +317,10 @@ static void test_cancel_ready(void)
     cancel_common(s);
 }
 
+/*
+ * This test always runs in the main loop, so there is no
+ * need to protect job->status.
+ */
 static void test_cancel_standby(void)
 {
     Job *job;
@@ -312,13 +335,19 @@ static void test_cancel_standby(void)
     job_enter(job);
     assert(job->status == JOB_STATUS_READY);
 
-    job_user_pause(job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_user_pause(job, &error_abort);
+    }
     job_enter(job);
     assert(job->status == JOB_STATUS_STANDBY);
 
     cancel_common(s);
 }
 
+/*
+ * This test always runs in the main loop, so there is no
+ * need to protect job->status.
+ */
 static void test_cancel_pending(void)
 {
     Job *job;
@@ -333,7 +362,9 @@ static void test_cancel_pending(void)
     job_enter(job);
     assert(job->status == JOB_STATUS_READY);
 
-    job_complete(job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_complete(job, &error_abort);
+    }
     job_enter(job);
     while (!job->deferred_to_main_loop) {
         aio_poll(qemu_get_aio_context(), true);
@@ -345,6 +376,10 @@ static void test_cancel_pending(void)
     cancel_common(s);
 }
 
+/*
+ * This test always runs in the main loop, so there is no
+ * need to protect job->status.
+ */
 static void test_cancel_concluded(void)
 {
     Job *job;
@@ -359,7 +394,9 @@ static void test_cancel_concluded(void)
     job_enter(job);
     assert(job->status == JOB_STATUS_READY);
 
-    job_complete(job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_complete(job, &error_abort);
+    }
     job_enter(job);
     while (!job->deferred_to_main_loop) {
         aio_poll(qemu_get_aio_context(), true);
@@ -369,7 +406,9 @@ static void test_cancel_concluded(void)
     assert(job->status == JOB_STATUS_PENDING);
 
     aio_context_acquire(job->aio_context);
-    job_finalize(job, &error_abort);
+    WITH_JOB_LOCK_GUARD() {
+        job_finalize(job, &error_abort);
+    }
     aio_context_release(job->aio_context);
     assert(job->status == JOB_STATUS_CONCLUDED);
 
@@ -459,36 +498,45 @@ static void test_complete_in_standby(void)
     bjob = mk_job(blk, "job", &test_yielding_driver, true,
                   JOB_MANUAL_FINALIZE | JOB_MANUAL_DISMISS);
     job = &bjob->job;
+    /* Job did not start, so status is safe to read*/
     assert(job->status == JOB_STATUS_CREATED);
 
     /* Wait for the job to become READY */
     job_start(job);
     aio_context_acquire(ctx);
+    /*
+     * Here we are waiting for the status to change, so don't bother
+     * protecting the read every time.
+     */
     AIO_WAIT_WHILE(ctx, job->status != JOB_STATUS_READY);
     aio_context_release(ctx);
 
     /* Begin the drained section, pausing the job */
     bdrv_drain_all_begin();
-    assert(job->status == JOB_STATUS_STANDBY);
+    WITH_JOB_LOCK_GUARD() {
+        assert(job->status == JOB_STATUS_STANDBY);
+    }
     /* Lock the IO thread to prevent the job from being run */
     aio_context_acquire(ctx);
     /* This will schedule the job to resume it */
     bdrv_drain_all_end();
 
-    /* But the job cannot run, so it will remain on standby */
-    assert(job->status == JOB_STATUS_STANDBY);
+    WITH_JOB_LOCK_GUARD() {
+        /* But the job cannot run, so it will remain on standby */
+        assert(job->status == JOB_STATUS_STANDBY);
 
-    /* Even though the job is on standby, this should work */
-    job_complete(job, &error_abort);
+        /* Even though the job is on standby, this should work */
+        job_complete(job, &error_abort);
 
-    /* The test is done now, clean up. */
-    job_finish_sync(job, NULL, &error_abort);
-    assert(job->status == JOB_STATUS_PENDING);
+        /* The test is done now, clean up. */
+        job_finish_sync(job, NULL, &error_abort);
+        assert(job->status == JOB_STATUS_PENDING);
 
-    job_finalize(job, &error_abort);
-    assert(job->status == JOB_STATUS_CONCLUDED);
+        job_finalize(job, &error_abort);
+        assert(job->status == JOB_STATUS_CONCLUDED);
 
-    job_dismiss(&job, &error_abort);
+        job_dismiss(&job, &error_abort);
+    }
 
     destroy_blk(blk);
     aio_context_release(ctx);
-- 
2.31.1

[PATCH v5 11/20] block/mirror.c: use of job helpers in drivers to avoid TOC/TOU

[Emanuele Giuseppe Esposito]

Once job lock is used and aiocontext is removed, mirror has
to perform job operations under the same critical section,
using the helpers prepared in previous commit.

Note: at this stage, job_{lock/unlock} and job lock guard macros
are *nop*.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/mirror.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index bfc3ac1f77..57f19e09dd 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -653,9 +653,13 @@ static int mirror_exit_common(Job *job)
     BlockDriverState *target_bs;
     BlockDriverState *mirror_top_bs;
     Error *local_err = NULL;
-    bool abort = job->ret < 0;
+    bool abort;
     int ret = 0;
 
+    WITH_JOB_LOCK_GUARD() {
+        abort = job->ret < 0;
+    }
+
     if (s->prepared) {
         return 0;
     }
@@ -1151,8 +1155,10 @@ static void mirror_complete(Job *job, Error **errp)
     s->should_complete = true;
 
     /* If the job is paused, it will be re-entered when it is resumed */
-    if (!job->paused) {
-        job_enter(job);
+    WITH_JOB_LOCK_GUARD() {
+        if (!job->paused) {
+            job_enter_cond(job, NULL);
+        }
     }
 }
 
@@ -1172,8 +1178,11 @@ static bool mirror_drained_poll(BlockJob *job)
      * from one of our own drain sections, to avoid a deadlock waiting for
      * ourselves.
      */
-    if (!s->common.job.paused && !job_is_cancelled(&job->job) && !s->in_drain) {
-        return true;
+    WITH_JOB_LOCK_GUARD() {
+        if (!s->common.job.paused && !job_is_cancelled_locked(&job->job)
+            && !s->in_drain) {
+            return true;
+        }
     }
 
     return !!s->in_flight;
-- 
2.31.1

Re: [PATCH v5 11/20] block/mirror.c: use of job helpers in drivers to avoid TOC/TOU

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 715 bytes --]

On Tue, Feb 08, 2022 at 09:35:04AM -0500, Emanuele Giuseppe Esposito wrote:
> Once job lock is used and aiocontext is removed, mirror has
> to perform job operations under the same critical section,
> using the helpers prepared in previous commit.
> 
> Note: at this stage, job_{lock/unlock} and job lock guard macros
> are *nop*.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  block/mirror.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)

My understanding is that MirrorBlockJob itself does need a lock because
it's only access from the coroutines - and they run in only one thread.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

[PATCH v5 12/20] jobs: rename static functions called with job_mutex held

[Emanuele Giuseppe Esposito]

With the *nop* job_lock/unlock placed, rename the static
functions that are always under job_mutex, adding "_locked" suffix.

List of functions that get this suffix:
job_txn_ref		   job_txn_del_job
job_txn_apply		   job_state_transition
job_should_pause	   job_event_cancelled
job_event_completed	   job_event_pending
job_event_ready		   job_event_idle
job_do_yield		   job_timer_not_pending
job_do_dismiss		   job_conclude
job_update_rc		   job_commit
job_abort		   job_clean
job_finalize_single	   job_cancel_async
job_completed_txn_abort	   job_prepare
job_needs_finalize	   job_do_finalize
job_transition_to_pending  job_completed_txn_success
job_completed		   job_cancel_err
job_force_cancel_err

Note that "locked" refers to the *nop* job_lock/unlock, and not
real_job_lock/unlock.

No functional change intended.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 job.c | 247 +++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 141 insertions(+), 106 deletions(-)

diff --git a/job.c b/job.c
index 75f7c28147..56d2a8d98f 100644
--- a/job.c
+++ b/job.c
@@ -113,7 +113,8 @@ JobTxn *job_txn_new(void)
     return txn;
 }
 
-static void job_txn_ref(JobTxn *txn)
+/* Called with job_mutex held. */
+static void job_txn_ref_locked(JobTxn *txn)
 {
     txn->refcnt++;
 }
@@ -135,10 +136,11 @@ static void job_txn_add_job(JobTxn *txn, Job *job)
     job->txn = txn;
 
     QLIST_INSERT_HEAD(&txn->jobs, job, txn_list);
-    job_txn_ref(txn);
+    job_txn_ref_locked(txn);
 }
 
-static void job_txn_del_job(Job *job)
+/* Called with job_mutex held. */
+static void job_txn_del_job_locked(Job *job)
 {
     if (job->txn) {
         QLIST_REMOVE(job, txn_list);
@@ -147,17 +149,18 @@ static void job_txn_del_job(Job *job)
     }
 }
 
-static int job_txn_apply(Job *job, int fn(Job *))
+/* Called with job_mutex held. */
+static int job_txn_apply_locked(Job *job, int fn(Job *))
 {
     Job *other_job, *next;
     JobTxn *txn = job->txn;
     int rc = 0;
 
     /*
-     * Similar to job_completed_txn_abort, we take each job's lock before
-     * applying fn, but since we assume that outer_ctx is held by the caller,
-     * we need to release it here to avoid holding the lock twice - which would
-     * break AIO_WAIT_WHILE from within fn.
+     * Similar to job_completed_txn_abort_locked, we take each job's lock
+     * before applying fn, but since we assume that outer_ctx is held by
+     * the caller, we need to release it here to avoid holding the lock
+     * twice - which would break AIO_WAIT_WHILE from within fn.
      */
     job_ref(job);
     aio_context_release(job->aio_context);
@@ -183,7 +186,8 @@ bool job_is_internal(Job *job)
     return (job->id == NULL);
 }
 
-static void job_state_transition(Job *job, JobStatus s1)
+/* Called with job_mutex held. */
+static void job_state_transition_locked(Job *job, JobStatus s1)
 {
     JobStatus s0 = job->status;
     assert(s1 >= 0 && s1 < JOB_STATUS__MAX);
@@ -308,7 +312,8 @@ static bool job_started(Job *job)
     return job->co;
 }
 
-static bool job_should_pause(Job *job)
+/* Called with job_mutex held. */
+static bool job_should_pause_locked(Job *job)
 {
     return job->pause_count > 0;
 }
@@ -388,7 +393,7 @@ void *job_create(const char *job_id, const JobDriver *driver, JobTxn *txn,
     notifier_list_init(&job->on_ready);
     notifier_list_init(&job->on_idle);
 
-    job_state_transition(job, JOB_STATUS_CREATED);
+    job_state_transition_locked(job, JOB_STATUS_CREATED);
     aio_timer_init(qemu_get_aio_context(), &job->sleep_timer,
                    QEMU_CLOCK_REALTIME, SCALE_NS,
                    job_sleep_timer_cb, job);
@@ -454,31 +459,36 @@ void job_progress_increase_remaining(Job *job, uint64_t delta)
 
 /**
  * To be called when a cancelled job is finalised.
+ * Called with job_mutex held.
  */
-static void job_event_cancelled(Job *job)
+static void job_event_cancelled_locked(Job *job)
 {
     notifier_list_notify(&job->on_finalize_cancelled, job);
 }
 
 /**
  * To be called when a successfully completed job is finalised.
+ * Called with job_mutex held.
  */
-static void job_event_completed(Job *job)
+static void job_event_completed_locked(Job *job)
 {
     notifier_list_notify(&job->on_finalize_completed, job);
 }
 
-static void job_event_pending(Job *job)
+/* Called with job_mutex held. */
+static void job_event_pending_locked(Job *job)
 {
     notifier_list_notify(&job->on_pending, job);
 }
 
-static void job_event_ready(Job *job)
+/* Called with job_mutex held. */
+static void job_event_ready_locked(Job *job)
 {
     notifier_list_notify(&job->on_ready, job);
 }
 
-static void job_event_idle(Job *job)
+/* Called with job_mutex held. */
+static void job_event_idle_locked(Job *job)
 {
     notifier_list_notify(&job->on_idle, job);
 }
@@ -516,20 +526,24 @@ void job_enter(Job *job)
     job_enter_cond(job, NULL);
 }
 
-/* Yield, and schedule a timer to reenter the coroutine after @ns nanoseconds.
+/*
+ * Yield, and schedule a timer to reenter the coroutine after @ns nanoseconds.
  * Reentering the job coroutine with job_enter() before the timer has expired
  * is allowed and cancels the timer.
  *
  * If @ns is (uint64_t) -1, no timer is scheduled and job_enter() must be
- * called explicitly. */
-static void coroutine_fn job_do_yield(Job *job, uint64_t ns)
+ * called explicitly.
+ *
+ * Called with job_mutex held, but releases it temporarly.
+ */
+static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns)
 {
     real_job_lock();
     if (ns != -1) {
         timer_mod(&job->sleep_timer, ns);
     }
     job->busy = false;
-    job_event_idle(job);
+    job_event_idle_locked(job);
     real_job_unlock();
     job_unlock();
     qemu_coroutine_yield();
@@ -544,7 +558,7 @@ static void coroutine_fn job_pause_point_locked(Job *job)
 {
     assert(job && job_started(job));
 
-    if (!job_should_pause(job)) {
+    if (!job_should_pause_locked(job)) {
         return;
     }
     if (job_is_cancelled_locked(job)) {
@@ -557,15 +571,15 @@ static void coroutine_fn job_pause_point_locked(Job *job)
         job_lock();
     }
 
-    if (job_should_pause(job) && !job_is_cancelled_locked(job)) {
+    if (job_should_pause_locked(job) && !job_is_cancelled_locked(job)) {
         JobStatus status = job->status;
-        job_state_transition(job, status == JOB_STATUS_READY
-                                  ? JOB_STATUS_STANDBY
-                                  : JOB_STATUS_PAUSED);
+        job_state_transition_locked(job, status == JOB_STATUS_READY
+                                    ? JOB_STATUS_STANDBY
+                                    : JOB_STATUS_PAUSED);
         job->paused = true;
-        job_do_yield(job, -1);
+        job_do_yield_locked(job, -1);
         job->paused = false;
-        job_state_transition(job, status);
+        job_state_transition_locked(job, status);
     }
 
     if (job->driver->resume) {
@@ -591,8 +605,8 @@ void job_yield(Job *job)
         return;
     }
 
-    if (!job_should_pause(job)) {
-        job_do_yield(job, -1);
+    if (!job_should_pause_locked(job)) {
+        job_do_yield_locked(job, -1);
     }
 
     job_pause_point_locked(job);
@@ -608,15 +622,15 @@ void coroutine_fn job_sleep_ns(Job *job, int64_t ns)
         return;
     }
 
-    if (!job_should_pause(job)) {
-        job_do_yield(job, qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + ns);
+    if (!job_should_pause_locked(job)) {
+        job_do_yield_locked(job, qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + ns);
     }
 
     job_pause_point_locked(job);
 }
 
 /* Assumes the job_mutex is held */
-static bool job_timer_not_pending(Job *job)
+static bool job_timer_not_pending_locked(Job *job)
 {
     return !timer_pending(&job->sleep_timer);
 }
@@ -638,7 +652,7 @@ void job_resume(Job *job)
     }
 
     /* kick only if no timer is pending */
-    job_enter_cond(job, job_timer_not_pending);
+    job_enter_cond(job, job_timer_not_pending_locked);
 }
 
 void job_user_pause(Job *job, Error **errp)
@@ -679,16 +693,17 @@ void job_user_resume(Job *job, Error **errp)
     job_resume(job);
 }
 
-static void job_do_dismiss(Job *job)
+/* Called with job_mutex held. */
+static void job_do_dismiss_locked(Job *job)
 {
     assert(job);
     job->busy = false;
     job->paused = false;
     job->deferred_to_main_loop = true;
 
-    job_txn_del_job(job);
+    job_txn_del_job_locked(job);
 
-    job_state_transition(job, JOB_STATUS_NULL);
+    job_state_transition_locked(job, JOB_STATUS_NULL);
     job_unref(job);
 }
 
@@ -701,7 +716,7 @@ void job_dismiss(Job **jobptr, Error **errp)
         return;
     }
 
-    job_do_dismiss(job);
+    job_do_dismiss_locked(job);
     *jobptr = NULL;
 }
 
@@ -709,18 +724,20 @@ void job_early_fail(Job *job)
 {
     JOB_LOCK_GUARD();
     assert(job->status == JOB_STATUS_CREATED);
-    job_do_dismiss(job);
+    job_do_dismiss_locked(job);
 }
 
-static void job_conclude(Job *job)
+/* Called with job_mutex held. */
+static void job_conclude_locked(Job *job)
 {
-    job_state_transition(job, JOB_STATUS_CONCLUDED);
+    job_state_transition_locked(job, JOB_STATUS_CONCLUDED);
     if (job->auto_dismiss || !job_started(job)) {
-        job_do_dismiss(job);
+        job_do_dismiss_locked(job);
     }
 }
 
-static void job_update_rc(Job *job)
+/* Called with job_mutex held. */
+static void job_update_rc_locked(Job *job)
 {
     if (!job->ret && job_is_cancelled_locked(job)) {
         job->ret = -ECANCELED;
@@ -729,11 +746,12 @@ static void job_update_rc(Job *job)
         if (!job->err) {
             error_setg(&job->err, "%s", strerror(-job->ret));
         }
-        job_state_transition(job, JOB_STATUS_ABORTING);
+        job_state_transition_locked(job, JOB_STATUS_ABORTING);
     }
 }
 
-static void job_commit(Job *job)
+/* Called with job_mutex held, but releases it temporarly. */
+static void job_commit_locked(Job *job)
 {
     assert(!job->ret);
     assert(qemu_in_main_thread());
@@ -744,7 +762,8 @@ static void job_commit(Job *job)
     }
 }
 
-static void job_abort(Job *job)
+/* Called with job_mutex held, but releases it temporarly. */
+static void job_abort_locked(Job *job)
 {
     assert(job->ret);
     assert(qemu_in_main_thread());
@@ -755,7 +774,8 @@ static void job_abort(Job *job)
     }
 }
 
-static void job_clean(Job *job)
+/* Called with job_mutex held, but releases it temporarly. */
+static void job_clean_locked(Job *job)
 {
     assert(qemu_in_main_thread());
     if (job->driver->clean) {
@@ -765,7 +785,8 @@ static void job_clean(Job *job)
     }
 }
 
-static int job_finalize_single(Job *job)
+/* Called with job_mutex held, but releases it temporarly. */
+static int job_finalize_single_locked(Job *job)
 {
     int job_ret;
     AioContext *ctx = job->aio_context;
@@ -773,16 +794,16 @@ static int job_finalize_single(Job *job)
     assert(job_is_completed_locked(job));
 
     /* Ensure abort is called for late-transactional failures */
-    job_update_rc(job);
+    job_update_rc_locked(job);
 
     aio_context_acquire(ctx);
 
     if (!job->ret) {
-        job_commit(job);
+        job_commit_locked(job);
     } else {
-        job_abort(job);
+        job_abort_locked(job);
     }
-    job_clean(job);
+    job_clean_locked(job);
 
     aio_context_release(ctx);
 
@@ -796,18 +817,19 @@ static int job_finalize_single(Job *job)
     /* Emit events only if we actually started */
     if (job_started(job)) {
         if (job_is_cancelled_locked(job)) {
-            job_event_cancelled(job);
+            job_event_cancelled_locked(job);
         } else {
-            job_event_completed(job);
+            job_event_completed_locked(job);
         }
     }
 
-    job_txn_del_job(job);
-    job_conclude(job);
+    job_txn_del_job_locked(job);
+    job_conclude_locked(job);
     return 0;
 }
 
-static void job_cancel_async(Job *job, bool force)
+/* Called with job_mutex held, but releases it temporarly. */
+static void job_cancel_async_locked(Job *job, bool force)
 {
     assert(qemu_in_main_thread());
     if (job->driver->cancel) {
@@ -845,7 +867,8 @@ static void job_cancel_async(Job *job, bool force)
     }
 }
 
-static void job_completed_txn_abort(Job *job)
+/* Called with job_mutex held. */
+static void job_completed_txn_abort_locked(Job *job)
 {
     AioContext *ctx;
     JobTxn *txn = job->txn;
@@ -858,12 +881,12 @@ static void job_completed_txn_abort(Job *job)
         return;
     }
     txn->aborting = true;
-    job_txn_ref(txn);
+    job_txn_ref_locked(txn);
 
     /*
      * We can only hold the single job's AioContext lock while calling
-     * job_finalize_single() because the finalization callbacks can involve
-     * calls of AIO_WAIT_WHILE(), which could deadlock otherwise.
+     * job_finalize_single_locked() because the finalization callbacks can
+     * involve calls of AIO_WAIT_WHILE(), which could deadlock otherwise.
      * Note that the job's AioContext may change when it is finalized.
      */
     job_ref(job);
@@ -881,7 +904,7 @@ static void job_completed_txn_abort(Job *job)
              * Therefore, pass force=true to terminate all other jobs as quickly
              * as possible.
              */
-            job_cancel_async(other_job, true);
+            job_cancel_async_locked(other_job, true);
             aio_context_release(ctx);
         }
     }
@@ -898,12 +921,12 @@ static void job_completed_txn_abort(Job *job)
             job_finish_sync(other_job, NULL, NULL);
         }
         aio_context_release(ctx);
-        job_finalize_single(other_job);
+        job_finalize_single_locked(other_job);
     }
 
     /*
      * Use job_ref()/job_unref() so we can read the AioContext here
-     * even if the job went away during job_finalize_single().
+     * even if the job went away during job_finalize_single_locked().
      */
     aio_context_acquire(job->aio_context);
     job_unref(job);
@@ -911,7 +934,8 @@ static void job_completed_txn_abort(Job *job)
     job_txn_unref(txn);
 }
 
-static int job_prepare(Job *job)
+/* Called with job_mutex held, but releases it temporarly. */
+static int job_prepare_locked(Job *job)
 {
     int ret;
     AioContext *ctx = job->aio_context;
@@ -924,28 +948,30 @@ static int job_prepare(Job *job)
         aio_context_release(ctx);
         job_lock();
         job->ret = ret;
-        job_update_rc(job);
+        job_update_rc_locked(job);
     }
 
     return job->ret;
 }
 
-static int job_needs_finalize(Job *job)
+/* Called with job_mutex held. */
+static int job_needs_finalize_locked(Job *job)
 {
     return !job->auto_finalize;
 }
 
-static void job_do_finalize(Job *job)
+/* Called with job_mutex held. */
+static void job_do_finalize_locked(Job *job)
 {
     int rc;
     assert(job && job->txn);
 
     /* prepare the transaction to complete */
-    rc = job_txn_apply(job, job_prepare);
+    rc = job_txn_apply_locked(job, job_prepare_locked);
     if (rc) {
-        job_completed_txn_abort(job);
+        job_completed_txn_abort_locked(job);
     } else {
-        job_txn_apply(job, job_finalize_single);
+        job_txn_apply_locked(job, job_finalize_single_locked);
     }
 }
 
@@ -955,14 +981,15 @@ void job_finalize(Job *job, Error **errp)
     if (job_apply_verb(job, JOB_VERB_FINALIZE, errp)) {
         return;
     }
-    job_do_finalize(job);
+    job_do_finalize_locked(job);
 }
 
-static int job_transition_to_pending(Job *job)
+/* Called with job_mutex held. */
+static int job_transition_to_pending_locked(Job *job)
 {
-    job_state_transition(job, JOB_STATUS_PENDING);
+    job_state_transition_locked(job, JOB_STATUS_PENDING);
     if (!job->auto_finalize) {
-        job_event_pending(job);
+        job_event_pending_locked(job);
     }
     return 0;
 }
@@ -970,16 +997,17 @@ static int job_transition_to_pending(Job *job)
 void job_transition_to_ready(Job *job)
 {
     JOB_LOCK_GUARD();
-    job_state_transition(job, JOB_STATUS_READY);
-    job_event_ready(job);
+    job_state_transition_locked(job, JOB_STATUS_READY);
+    job_event_ready_locked(job);
 }
 
-static void job_completed_txn_success(Job *job)
+/* Called with job_mutex held. */
+static void job_completed_txn_success_locked(Job *job)
 {
     JobTxn *txn = job->txn;
     Job *other_job;
 
-    job_state_transition(job, JOB_STATUS_WAITING);
+    job_state_transition_locked(job, JOB_STATUS_WAITING);
 
     /*
      * Successful completion, see if there are other running jobs in this
@@ -992,24 +1020,25 @@ static void job_completed_txn_success(Job *job)
         assert(other_job->ret == 0);
     }
 
-    job_txn_apply(job, job_transition_to_pending);
+    job_txn_apply_locked(job, job_transition_to_pending_locked);
 
     /* If no jobs need manual finalization, automatically do so */
-    if (job_txn_apply(job, job_needs_finalize) == 0) {
-        job_do_finalize(job);
+    if (job_txn_apply_locked(job, job_needs_finalize_locked) == 0) {
+        job_do_finalize_locked(job);
     }
 }
 
-static void job_completed(Job *job)
+/* Called with job_mutex held. */
+static void job_completed_locked(Job *job)
 {
     assert(job && job->txn && !job_is_completed_locked(job));
 
-    job_update_rc(job);
+    job_update_rc_locked(job);
     trace_job_completed(job, job->ret);
     if (job->ret) {
-        job_completed_txn_abort(job);
+        job_completed_txn_abort_locked(job);
     } else {
-        job_completed_txn_success(job);
+        job_completed_txn_success_locked(job);
     }
 }
 
@@ -1031,15 +1060,16 @@ static void job_exit(void *opaque)
      * drain block nodes, and if .drained_poll still returned true, we would
      * deadlock. */
     job->busy = false;
-    job_event_idle(job);
+    job_event_idle_locked(job);
 
-    job_completed(job);
+    job_completed_locked(job);
 
     /*
-     * Note that calling job_completed can move the job to a different
-     * aio_context, so we cannot cache from above. job_txn_apply takes care of
-     * acquiring the new lock, and we ref/unref to avoid job_completed freeing
-     * the job underneath us.
+     * Note that calling job_completed_locked can move the job to a different
+     * aio_context, so we cannot cache from above.
+     * job_txn_apply_locked takes care of
+     * acquiring the new lock, and we ref/unref to avoid job_completed_locked
+     * freeing the job underneath us.
      */
     ctx = job->aio_context;
     job_unref(job);
@@ -1078,7 +1108,7 @@ void job_start(Job *job)
         job->pause_count--;
         job->busy = true;
         job->paused = false;
-        job_state_transition(job, JOB_STATUS_RUNNING);
+        job_state_transition_locked(job, JOB_STATUS_RUNNING);
     }
     aio_co_enter(job->aio_context, job->co);
 }
@@ -1086,25 +1116,25 @@ void job_start(Job *job)
 void job_cancel(Job *job, bool force)
 {
     if (job->status == JOB_STATUS_CONCLUDED) {
-        job_do_dismiss(job);
+        job_do_dismiss_locked(job);
         return;
     }
-    job_cancel_async(job, force);
+    job_cancel_async_locked(job, force);
     if (!job_started(job)) {
-        job_completed(job);
+        job_completed_locked(job);
     } else if (job->deferred_to_main_loop) {
         /*
-         * job_cancel_async() ignores soft-cancel requests for jobs
+         * job_cancel_async_locked() ignores soft-cancel requests for jobs
          * that are already done (i.e. deferred to the main loop).  We
          * have to check again whether the job is really cancelled.
          * (job_cancel_requested_locked() and job_is_cancelled_locked()
-         * are equivalent here, because job_cancel_async() will
+         * are equivalent here, because job_cancel_async_locked() will
          * make soft-cancel requests no-ops when deferred_to_main_loop is true.
          * We choose to call job_is_cancelled_locked() to show that we invoke
-         * job_completed_txn_abort() only for force-cancelled jobs.)
+         * job_completed_txn_abort_locked() only for force-cancelled jobs.)
          */
         if (job_is_cancelled_locked(job)) {
-            job_completed_txn_abort(job);
+            job_completed_txn_abort_locked(job);
         }
     } else {
         job_enter_cond(job, NULL);
@@ -1119,18 +1149,23 @@ void job_user_cancel(Job *job, bool force, Error **errp)
     job_cancel(job, force);
 }
 
-/* A wrapper around job_cancel() taking an Error ** parameter so it may be
+/*
+ * A wrapper around job_cancel() taking an Error ** parameter so it may be
  * used with job_finish_sync() without the need for (rather nasty) function
- * pointer casts there. */
-static void job_cancel_err(Job *job, Error **errp)
+ * pointer casts there.
+ *
+ * Called with job_mutex held.
+ */
+static void job_cancel_err_locked(Job *job, Error **errp)
 {
     job_cancel(job, false);
 }
 
 /**
- * Same as job_cancel_err(), but force-cancel.
+ * Same as job_cancel_err_locked(), but force-cancel.
+ * Called with job_mutex held.
  */
-static void job_force_cancel_err(Job *job, Error **errp)
+static void job_force_cancel_err_locked(Job *job, Error **errp)
 {
     job_cancel(job, true);
 }
@@ -1138,9 +1173,9 @@ static void job_force_cancel_err(Job *job, Error **errp)
 int job_cancel_sync(Job *job, bool force)
 {
     if (force) {
-        return job_finish_sync(job, &job_force_cancel_err, NULL);
+        return job_finish_sync(job, &job_force_cancel_err_locked, NULL);
     } else {
-        return job_finish_sync(job, &job_cancel_err, NULL);
+        return job_finish_sync(job, &job_cancel_err_locked, NULL);
     }
 }
 
-- 
2.31.1

[PATCH v5 13/20] job.h: rename job API functions called with job_mutex held

[Emanuele Giuseppe Esposito]

With the *nop* job_lock/unlock placed, rename the job functions
of the job API that are always under job_mutex, adding "_locked"
suffix.

List of functions that get this suffix:
job_txn_unref		job_txn_add_job
job_ref			job_unref
job_enter_cond		job_finish_sync
job_is_ready		job_pause
job_resume		job_user_pause
job_user_paused		job_user_resume
job_next		job_get
job_apply_verb		job_complete
job_cancel		job_user_cancel
job_cancel_sync		job_complete_sync
job_finalize		job_dismiss

Note that "locked" refers to the *nop* job_lock/unlock, and not
real_job_lock/unlock.

No functional change intended.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block.c                          |   2 +-
 block/mirror.c                   |   2 +-
 block/replication.c              |   4 +-
 blockdev.c                       |  32 ++++----
 blockjob.c                       |  14 ++--
 include/qemu/job.h               | 119 ++++++++++++++++++----------
 job-qmp.c                        |  26 +++----
 job.c                            | 129 ++++++++++++++++---------------
 qemu-img.c                       |   6 +-
 tests/unit/test-bdrv-drain.c     |   2 +-
 tests/unit/test-block-iothread.c |   4 +-
 tests/unit/test-blockjob-txn.c   |  14 ++--
 tests/unit/test-blockjob.c       |  30 +++----
 13 files changed, 213 insertions(+), 171 deletions(-)

diff --git a/block.c b/block.c
index 33fe969fd9..1edb59aaae 100644
--- a/block.c
+++ b/block.c
@@ -4969,7 +4969,7 @@ static void bdrv_close(BlockDriverState *bs)
 void bdrv_close_all(void)
 {
     WITH_JOB_LOCK_GUARD() {
-        assert(job_next(NULL) == NULL);
+        assert(job_next_locked(NULL) == NULL);
     }
     assert(qemu_in_main_thread());
 
diff --git a/block/mirror.c b/block/mirror.c
index 57f19e09dd..0a3eb712e6 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1157,7 +1157,7 @@ static void mirror_complete(Job *job, Error **errp)
     /* If the job is paused, it will be re-entered when it is resumed */
     WITH_JOB_LOCK_GUARD() {
         if (!job->paused) {
-            job_enter_cond(job, NULL);
+            job_enter_cond_locked(job, NULL);
         }
     }
 }
diff --git a/block/replication.c b/block/replication.c
index a03b28726e..50ea778937 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -150,7 +150,7 @@ static void replication_close(BlockDriverState *bs)
         commit_job = &s->commit_job->job;
         assert(commit_job->aio_context == qemu_get_current_aio_context());
         WITH_JOB_LOCK_GUARD() {
-            job_cancel_sync(commit_job, false);
+            job_cancel_sync_locked(commit_job, false);
         }
     }
 
@@ -729,7 +729,7 @@ static void replication_stop(ReplicationState *rs, bool failover, Error **errp)
          */
         if (s->backup_job) {
             WITH_JOB_LOCK_GUARD() {
-                job_cancel_sync(&s->backup_job->job, true);
+                job_cancel_sync_locked(&s->backup_job->job, true);
             }
         }
 
diff --git a/blockdev.c b/blockdev.c
index 08408cd44b..4bcb09ad9e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -157,7 +157,7 @@ void blockdev_mark_auto_del(BlockBackend *blk)
             AioContext *aio_context = job->job.aio_context;
             aio_context_acquire(aio_context);
 
-            job_cancel(&job->job, false);
+            job_cancel_locked(&job->job, false);
 
             aio_context_release(aio_context);
         }
@@ -1841,7 +1841,7 @@ static void drive_backup_abort(BlkActionState *common)
         aio_context_acquire(aio_context);
 
         WITH_JOB_LOCK_GUARD() {
-            job_cancel_sync(&state->job->job, true);
+            job_cancel_sync_locked(&state->job->job, true);
         }
 
         aio_context_release(aio_context);
@@ -1944,7 +1944,7 @@ static void blockdev_backup_abort(BlkActionState *common)
         aio_context_acquire(aio_context);
 
         WITH_JOB_LOCK_GUARD() {
-            job_cancel_sync(&state->job->job, true);
+            job_cancel_sync_locked(&state->job->job, true);
         }
 
         aio_context_release(aio_context);
@@ -2396,7 +2396,7 @@ exit:
     }
 
     WITH_JOB_LOCK_GUARD() {
-        job_txn_unref(block_job_txn);
+        job_txn_unref_locked(block_job_txn);
     }
 }
 
@@ -3368,14 +3368,14 @@ void qmp_block_job_cancel(const char *device,
         force = false;
     }
 
-    if (job_user_paused(&job->job) && !force) {
+    if (job_user_paused_locked(&job->job) && !force) {
         error_setg(errp, "The block job for device '%s' is currently paused",
                    device);
         goto out;
     }
 
     trace_qmp_block_job_cancel(job);
-    job_user_cancel(&job->job, force, errp);
+    job_user_cancel_locked(&job->job, force, errp);
 out:
     aio_context_release(aio_context);
     job_unlock();
@@ -3391,7 +3391,7 @@ void qmp_block_job_pause(const char *device, Error **errp)
     }
 
     trace_qmp_block_job_pause(job);
-    job_user_pause(&job->job, errp);
+    job_user_pause_locked(&job->job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -3406,7 +3406,7 @@ void qmp_block_job_resume(const char *device, Error **errp)
     }
 
     trace_qmp_block_job_resume(job);
-    job_user_resume(&job->job, errp);
+    job_user_resume_locked(&job->job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -3421,7 +3421,7 @@ void qmp_block_job_complete(const char *device, Error **errp)
     }
 
     trace_qmp_block_job_complete(job);
-    job_complete(&job->job, errp);
+    job_complete_locked(&job->job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -3436,16 +3436,16 @@ void qmp_block_job_finalize(const char *id, Error **errp)
     }
 
     trace_qmp_block_job_finalize(job);
-    job_ref(&job->job);
-    job_finalize(&job->job, errp);
+    job_ref_locked(&job->job);
+    job_finalize_locked(&job->job, errp);
 
     /*
-     * Job's context might have changed via job_finalize (and job_txn_apply
-     * automatically acquires the new one), so make sure we release the correct
-     * one.
+     * Job's context might have changed via job_finalize_locked
+     * (and job_txn_apply automatically acquires the new one),
+     * so make sure we release the correct one.
      */
     aio_context = block_job_get_aio_context(job);
-    job_unref(&job->job);
+    job_unref_locked(&job->job);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -3462,7 +3462,7 @@ void qmp_block_job_dismiss(const char *id, Error **errp)
 
     trace_qmp_block_job_dismiss(bjob);
     job = &bjob->job;
-    job_dismiss(&job, errp);
+    job_dismiss_locked(&job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
diff --git a/blockjob.c b/blockjob.c
index 5fb477fe26..c9b811e911 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -65,7 +65,7 @@ BlockJob *block_job_next(BlockJob *bjob)
     assert(qemu_in_main_thread());
 
     do {
-        job = job_next(job);
+        job = job_next_locked(job);
     } while (job && !is_block_job(job));
 
     return job ? container_of(job, BlockJob, job) : NULL;
@@ -73,7 +73,7 @@ BlockJob *block_job_next(BlockJob *bjob)
 
 BlockJob *block_job_get(const char *id)
 {
-    Job *job = job_get(id);
+    Job *job = job_get_locked(id);
     assert(qemu_in_main_thread());
 
     if (job && is_block_job(job)) {
@@ -103,7 +103,7 @@ static void child_job_drained_begin(BdrvChild *c)
 {
     BlockJob *job = c->opaque;
     WITH_JOB_LOCK_GUARD() {
-        job_pause(&job->job);
+        job_pause_locked(&job->job);
     }
 }
 
@@ -135,7 +135,7 @@ static void child_job_drained_end(BdrvChild *c, int *drained_end_counter)
 {
     BlockJob *job = c->opaque;
     WITH_JOB_LOCK_GUARD() {
-        job_resume(&job->job);
+        job_resume_locked(&job->job);
     }
 }
 
@@ -290,7 +290,7 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
 
     assert(qemu_in_main_thread());
 
-    if (job_apply_verb(&job->job, JOB_VERB_SET_SPEED, errp) < 0) {
+    if (job_apply_verb_locked(&job->job, JOB_VERB_SET_SPEED, errp) < 0) {
         return false;
     }
     if (speed < 0) {
@@ -314,7 +314,7 @@ bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
     }
 
     /* kick only if a timer is pending */
-    job_enter_cond(&job->job, job_timer_pending);
+    job_enter_cond_locked(&job->job, job_timer_pending);
 
     return true;
 }
@@ -568,7 +568,7 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockdevOnError on_err,
     if (action == BLOCK_ERROR_ACTION_STOP) {
         WITH_JOB_LOCK_GUARD() {
             if (!job->job.user_paused) {
-                job_pause(&job->job);
+                job_pause_locked(&job->job);
                 /*
                  * make the pause user visible, which will be
                  * resumed from QMP.
diff --git a/include/qemu/job.h b/include/qemu/job.h
index aa33d091b1..dfd2586e63 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -339,7 +339,7 @@ void job_unlock(void);
 
 /**
  * Allocate and return a new job transaction. Jobs can be added to the
- * transaction using job_txn_add_job().
+ * transaction using job_txn_add_job_locked().
  *
  * The transaction is automatically freed when the last job completes or is
  * cancelled.
@@ -351,10 +351,12 @@ void job_unlock(void);
 JobTxn *job_txn_new(void);
 
 /**
- * Release a reference that was previously acquired with job_txn_add_job or
- * job_txn_new. If it's the last reference to the object, it will be freed.
+ * Release a reference that was previously acquired with job_txn_add_job_locked
+ * or job_txn_new. If it's the last reference to the object, it will be freed.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_txn_unref(JobTxn *txn);
+void job_txn_unref_locked(JobTxn *txn);
 
 /**
  * Create a new long-running job and return it.
@@ -373,16 +375,20 @@ void *job_create(const char *job_id, const JobDriver *driver, JobTxn *txn,
                  void *opaque, Error **errp);
 
 /**
- * Add a reference to Job refcnt, it will be decreased with job_unref, and then
- * be freed if it comes to be the last reference.
+ * Add a reference to Job refcnt, it will be decreased with job_unref_locked,
+ * and then be freed if it comes to be the last reference.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_ref(Job *job);
+void job_ref_locked(Job *job);
 
 /**
- * Release a reference that was previously acquired with job_ref() or
+ * Release a reference that was previously acquired with job_ref_locked() or
  * job_create(). If it's the last reference to the object, it will be freed.
+ *
+ * Called between job_lock and job_unlock, but might release it temporarly.
  */
-void job_unref(Job *job);
+void job_unref_locked(Job *job);
 
 /**
  * @job: The job that has made progress
@@ -421,8 +427,10 @@ void job_progress_increase_remaining(Job *job, uint64_t delta);
  * Conditionally enter the job coroutine if the job is ready to run, not
  * already busy and fn() returns true. fn() is called while under the job_lock
  * critical section.
+ *
+ * Called between job_lock and job_unlock, but might release it temporarly.
  */
-void job_enter_cond(Job *job, bool(*fn)(Job *job));
+void job_enter_cond_locked(Job *job, bool(*fn)(Job *job));
 
 /**
  * @job: A job that has not yet been started.
@@ -442,8 +450,8 @@ void job_enter(Job *job);
 /**
  * @job: The job that is ready to pause.
  *
- * Pause now if job_pause() has been called. Jobs that perform lots of I/O
- * must call this between requests so that the job can be paused.
+ * Pause now if job_pause_locked() has been called. Jobs that perform lots of
+ * I/O must call this between requests so that the job can be paused.
  */
 void coroutine_fn job_pause_point(Job *job);
 
@@ -509,50 +517,68 @@ bool job_is_ready_locked(Job *job);
 
 /**
  * Request @job to pause at the next pause point. Must be paired with
- * job_resume(). If the job is supposed to be resumed by user action, call
- * job_user_pause() instead.
+ * job_resume_locked(). If the job is supposed to be resumed by user action,
+ * call job_user_pause_locked() instead.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_pause(Job *job);
+void job_pause_locked(Job *job);
 
-/** Resumes a @job paused with job_pause. */
-void job_resume(Job *job);
+/**
+ * Resumes a @job paused with job_pause_locked.
+ * Called between job_lock and job_unlock.
+ */
+void job_resume_locked(Job *job);
 
 /**
  * Asynchronously pause the specified @job.
- * Do not allow a resume until a matching call to job_user_resume.
+ * Do not allow a resume until a matching call to job_user_resume_locked.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_user_pause(Job *job, Error **errp);
+void job_user_pause_locked(Job *job, Error **errp);
 
-/** Returns true if the job is user-paused. */
-bool job_user_paused(Job *job);
+/**
+ * Returns true if the job is user-paused.
+ * Called between job_lock and job_unlock.
+ */
+bool job_user_paused_locked(Job *job);
 
 /**
  * Resume the specified @job.
- * Must be paired with a preceding job_user_pause.
+ * Must be paired with a preceding job_user_pause_locked.
+ *
+ * Called between job_lock and job_unlock, but might release it temporarly.
  */
-void job_user_resume(Job *job, Error **errp);
+void job_user_resume_locked(Job *job, Error **errp);
 
 /**
  * Get the next element from the list of block jobs after @job, or the
  * first one if @job is %NULL.
  *
  * Returns the requested job, or %NULL if there are no more jobs left.
+ *
+ * Called between job_lock and job_unlock.
  */
-Job *job_next(Job *job);
+Job *job_next_locked(Job *job);
 
 /**
  * Get the job identified by @id (which must not be %NULL).
  *
  * Returns the requested job, or %NULL if it doesn't exist.
+ *
+ * Called between job_lock and job_unlock.
  */
-Job *job_get(const char *id);
+Job *job_get_locked(const char *id);
 
 /**
  * Check whether the verb @verb can be applied to @job in its current state.
  * Returns 0 if the verb can be applied; otherwise errp is set and -EPERM
  * returned.
+ *
+ * Called between job_lock and job_unlock.
  */
-int job_apply_verb(Job *job, JobVerb verb, Error **errp);
+int job_apply_verb_locked(Job *job, JobVerb verb, Error **errp);
 
 /** The @job could not be started, free it. */
 void job_early_fail(Job *job);
@@ -560,20 +586,27 @@ void job_early_fail(Job *job);
 /** Moves the @job from RUNNING to READY */
 void job_transition_to_ready(Job *job);
 
-/** Asynchronously complete the specified @job. */
-void job_complete(Job *job, Error **errp);
+/**
+ * Asynchronously complete the specified @job.
+ * Called between job_lock and job_unlock, but it releases the lock temporarly.
+ */
+void job_complete_locked(Job *job, Error **errp);
 
 /**
  * Asynchronously cancel the specified @job. If @force is true, the job should
  * be cancelled immediately without waiting for a consistent state.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_cancel(Job *job, bool force);
+void job_cancel_locked(Job *job, bool force);
 
 /**
- * Cancels the specified job like job_cancel(), but may refuse to do so if the
- * operation isn't meaningful in the current state of the job.
+ * Cancels the specified job like job_cancel_locked(), but may refuse to do so
+ * if the operation isn't meaningful in the current state of the job.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_user_cancel(Job *job, bool force, Error **errp);
+void job_user_cancel_locked(Job *job, bool force, Error **errp);
 
 /**
  * Synchronously cancel the @job.  The completion callback is called
@@ -585,15 +618,16 @@ void job_user_cancel(Job *job, bool force, Error **errp);
  * during the call, or -ECANCELED if it was canceled.
  *
  * Callers must hold the AioContext lock of job->aio_context.
+ * Called between job_lock and job_unlock.
  */
-int job_cancel_sync(Job *job, bool force);
+int job_cancel_sync_locked(Job *job, bool force);
 
-/** Synchronously force-cancels all jobs using job_cancel_sync(). */
+/** Synchronously force-cancels all jobs using job_cancel_sync_locked(). */
 void job_cancel_sync_all(void);
 
 /**
  * @job: The job to be completed.
- * @errp: Error object which may be set by job_complete(); this is not
+ * @errp: Error object which may be set by job_complete_locked(); this is not
  *        necessarily set on every error, the job return value has to be
  *        checked as well.
  *
@@ -604,8 +638,9 @@ void job_cancel_sync_all(void);
  * Returns the return value from the job.
  *
  * Callers must hold the AioContext lock of job->aio_context.
+ * Called between job_lock and job_unlock.
  */
-int job_complete_sync(Job *job, Error **errp);
+int job_complete_sync_locked(Job *job, Error **errp);
 
 /**
  * For a @job that has finished its work and is pending awaiting explicit
@@ -614,14 +649,18 @@ int job_complete_sync(Job *job, Error **errp);
  * FIXME: Make the below statement universally true:
  * For jobs that support the manual workflow mode, all graph changes that occur
  * as a result will occur after this command and before a successful reply.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_finalize(Job *job, Error **errp);
+void job_finalize_locked(Job *job, Error **errp);
 
 /**
  * Remove the concluded @job from the query list and resets the passed pointer
  * to %NULL. Returns an error if the job is not actually concluded.
+ *
+ * Called between job_lock and job_unlock.
  */
-void job_dismiss(Job **job, Error **errp);
+void job_dismiss_locked(Job **job, Error **errp);
 
 /**
  * Synchronously finishes the given @job. If @finish is given, it is called to
@@ -631,7 +670,9 @@ void job_dismiss(Job **job, Error **errp);
  * cancelled before completing, and -errno in other error cases.
  *
  * Callers must hold the AioContext lock of job->aio_context.
+ * Called between job_lock and job_unlock.
  */
-int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp);
+int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
+                           Error **errp);
 
 #endif
diff --git a/job-qmp.c b/job-qmp.c
index a08cd7dd36..615e056fc4 100644
--- a/job-qmp.c
+++ b/job-qmp.c
@@ -40,7 +40,7 @@ static Job *find_job(const char *id, AioContext **aio_context, Error **errp)
     *aio_context = NULL;
     job_lock();
 
-    job = job_get(id);
+    job = job_get_locked(id);
     if (!job) {
         error_setg(errp, "Job not found");
         job_unlock();
@@ -63,7 +63,7 @@ void qmp_job_cancel(const char *id, Error **errp)
     }
 
     trace_qmp_job_cancel(job);
-    job_user_cancel(job, true, errp);
+    job_user_cancel_locked(job, true, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -78,7 +78,7 @@ void qmp_job_pause(const char *id, Error **errp)
     }
 
     trace_qmp_job_pause(job);
-    job_user_pause(job, errp);
+    job_user_pause_locked(job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -93,7 +93,7 @@ void qmp_job_resume(const char *id, Error **errp)
     }
 
     trace_qmp_job_resume(job);
-    job_user_resume(job, errp);
+    job_user_resume_locked(job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -108,7 +108,7 @@ void qmp_job_complete(const char *id, Error **errp)
     }
 
     trace_qmp_job_complete(job);
-    job_complete(job, errp);
+    job_complete_locked(job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -123,16 +123,16 @@ void qmp_job_finalize(const char *id, Error **errp)
     }
 
     trace_qmp_job_finalize(job);
-    job_ref(job);
-    job_finalize(job, errp);
+    job_ref_locked(job);
+    job_finalize_locked(job, errp);
 
     /*
-     * Job's context might have changed via job_finalize (and job_txn_apply
-     * automatically acquires the new one), so make sure we release the correct
-     * one.
+     * Job's context might have changed via job_finalize_locked
+     * (and job_txn_apply automatically acquires the new one),
+     * so make sure we release the correct one.
      */
     aio_context = job->aio_context;
-    job_unref(job);
+    job_unref_locked(job);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -147,7 +147,7 @@ void qmp_job_dismiss(const char *id, Error **errp)
     }
 
     trace_qmp_job_dismiss(job);
-    job_dismiss(&job, errp);
+    job_dismiss_locked(&job, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -184,7 +184,7 @@ JobInfoList *qmp_query_jobs(Error **errp)
 
     JOB_LOCK_GUARD();
 
-    for (job = job_next(NULL); job; job = job_next(job)) {
+    for (job = job_next_locked(NULL); job; job = job_next_locked(job)) {
         JobInfo *value;
 
         if (job_is_internal(job)) {
diff --git a/job.c b/job.c
index 56d2a8d98f..0ab25cb37e 100644
--- a/job.c
+++ b/job.c
@@ -119,14 +119,14 @@ static void job_txn_ref_locked(JobTxn *txn)
     txn->refcnt++;
 }
 
-void job_txn_unref(JobTxn *txn)
+void job_txn_unref_locked(JobTxn *txn)
 {
     if (txn && --txn->refcnt == 0) {
         g_free(txn);
     }
 }
 
-static void job_txn_add_job(JobTxn *txn, Job *job)
+static void job_txn_add_job_locked(JobTxn *txn, Job *job)
 {
     if (!txn) {
         return;
@@ -144,7 +144,7 @@ static void job_txn_del_job_locked(Job *job)
 {
     if (job->txn) {
         QLIST_REMOVE(job, txn_list);
-        job_txn_unref(job->txn);
+        job_txn_unref_locked(job->txn);
         job->txn = NULL;
     }
 }
@@ -162,7 +162,7 @@ static int job_txn_apply_locked(Job *job, int fn(Job *))
      * the caller, we need to release it here to avoid holding the lock
      * twice - which would break AIO_WAIT_WHILE from within fn.
      */
-    job_ref(job);
+    job_ref_locked(job);
     aio_context_release(job->aio_context);
 
     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
@@ -177,7 +177,7 @@ static int job_txn_apply_locked(Job *job, int fn(Job *))
      * can't use a local variable to cache it.
      */
     aio_context_acquire(job->aio_context);
-    job_unref(job);
+    job_unref_locked(job);
     return rc;
 }
 
@@ -202,7 +202,7 @@ static void job_state_transition_locked(Job *job, JobStatus s1)
     }
 }
 
-int job_apply_verb(Job *job, JobVerb verb, Error **errp)
+int job_apply_verb_locked(Job *job, JobVerb verb, Error **errp)
 {
     JobStatus s0 = job->status;
     assert(verb >= 0 && verb < JOB_VERB__MAX);
@@ -318,7 +318,7 @@ static bool job_should_pause_locked(Job *job)
     return job->pause_count > 0;
 }
 
-Job *job_next(Job *job)
+Job *job_next_locked(Job *job)
 {
     if (!job) {
         return QLIST_FIRST(&jobs);
@@ -326,7 +326,7 @@ Job *job_next(Job *job)
     return QLIST_NEXT(job, job_list);
 }
 
-Job *job_get(const char *id)
+Job *job_get_locked(const char *id)
 {
     Job *job;
 
@@ -363,7 +363,7 @@ void *job_create(const char *job_id, const JobDriver *driver, JobTxn *txn,
             error_setg(errp, "Invalid job ID '%s'", job_id);
             return NULL;
         }
-        if (job_get(job_id)) {
+        if (job_get_locked(job_id)) {
             error_setg(errp, "Job ID '%s' already in use", job_id);
             return NULL;
         }
@@ -404,21 +404,21 @@ void *job_create(const char *job_id, const JobDriver *driver, JobTxn *txn,
      * consolidating the job management logic */
     if (!txn) {
         txn = job_txn_new();
-        job_txn_add_job(txn, job);
-        job_txn_unref(txn);
+        job_txn_add_job_locked(txn, job);
+        job_txn_unref_locked(txn);
     } else {
-        job_txn_add_job(txn, job);
+        job_txn_add_job_locked(txn, job);
     }
 
     return job;
 }
 
-void job_ref(Job *job)
+void job_ref_locked(Job *job)
 {
     ++job->refcnt;
 }
 
-void job_unref(Job *job)
+void job_unref_locked(Job *job)
 {
     assert(qemu_in_main_thread());
 
@@ -493,7 +493,7 @@ static void job_event_idle_locked(Job *job)
     notifier_list_notify(&job->on_idle, job);
 }
 
-void job_enter_cond(Job *job, bool(*fn)(Job *job))
+void job_enter_cond_locked(Job *job, bool(*fn)(Job *job))
 {
     if (!job_started(job)) {
         return;
@@ -523,7 +523,7 @@ void job_enter_cond(Job *job, bool(*fn)(Job *job))
 void job_enter(Job *job)
 {
     JOB_LOCK_GUARD();
-    job_enter_cond(job, NULL);
+    job_enter_cond_locked(job, NULL);
 }
 
 /*
@@ -549,7 +549,7 @@ static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns)
     qemu_coroutine_yield();
     job_lock();
 
-    /* Set by job_enter_cond() before re-entering the coroutine.  */
+    /* Set by job_enter_cond_locked() before re-entering the coroutine.  */
     assert(job->busy);
 }
 
@@ -635,15 +635,15 @@ static bool job_timer_not_pending_locked(Job *job)
     return !timer_pending(&job->sleep_timer);
 }
 
-void job_pause(Job *job)
+void job_pause_locked(Job *job)
 {
     job->pause_count++;
     if (!job->paused) {
-        job_enter_cond(job, NULL);
+        job_enter_cond_locked(job, NULL);
     }
 }
 
-void job_resume(Job *job)
+void job_resume_locked(Job *job)
 {
     assert(job->pause_count > 0);
     job->pause_count--;
@@ -652,12 +652,12 @@ void job_resume(Job *job)
     }
 
     /* kick only if no timer is pending */
-    job_enter_cond(job, job_timer_not_pending_locked);
+    job_enter_cond_locked(job, job_timer_not_pending_locked);
 }
 
-void job_user_pause(Job *job, Error **errp)
+void job_user_pause_locked(Job *job, Error **errp)
 {
-    if (job_apply_verb(job, JOB_VERB_PAUSE, errp)) {
+    if (job_apply_verb_locked(job, JOB_VERB_PAUSE, errp)) {
         return;
     }
     if (job->user_paused) {
@@ -665,15 +665,15 @@ void job_user_pause(Job *job, Error **errp)
         return;
     }
     job->user_paused = true;
-    job_pause(job);
+    job_pause_locked(job);
 }
 
-bool job_user_paused(Job *job)
+bool job_user_paused_locked(Job *job)
 {
     return job->user_paused;
 }
 
-void job_user_resume(Job *job, Error **errp)
+void job_user_resume_locked(Job *job, Error **errp)
 {
     assert(job);
     assert(qemu_in_main_thread());
@@ -681,7 +681,7 @@ void job_user_resume(Job *job, Error **errp)
         error_setg(errp, "Can't resume a job that was not paused");
         return;
     }
-    if (job_apply_verb(job, JOB_VERB_RESUME, errp)) {
+    if (job_apply_verb_locked(job, JOB_VERB_RESUME, errp)) {
         return;
     }
     if (job->driver->user_resume) {
@@ -690,7 +690,7 @@ void job_user_resume(Job *job, Error **errp)
         job_lock();
     }
     job->user_paused = false;
-    job_resume(job);
+    job_resume_locked(job);
 }
 
 /* Called with job_mutex held. */
@@ -704,15 +704,15 @@ static void job_do_dismiss_locked(Job *job)
     job_txn_del_job_locked(job);
 
     job_state_transition_locked(job, JOB_STATUS_NULL);
-    job_unref(job);
+    job_unref_locked(job);
 }
 
-void job_dismiss(Job **jobptr, Error **errp)
+void job_dismiss_locked(Job **jobptr, Error **errp)
 {
     Job *job = *jobptr;
     /* similarly to _complete, this is QMP-interface only. */
     assert(job->id);
-    if (job_apply_verb(job, JOB_VERB_DISMISS, errp)) {
+    if (job_apply_verb_locked(job, JOB_VERB_DISMISS, errp)) {
         return;
     }
 
@@ -889,7 +889,7 @@ static void job_completed_txn_abort_locked(Job *job)
      * involve calls of AIO_WAIT_WHILE(), which could deadlock otherwise.
      * Note that the job's AioContext may change when it is finalized.
      */
-    job_ref(job);
+    job_ref_locked(job);
     aio_context_release(job->aio_context);
 
     /* Other jobs are effectively cancelled by us, set the status for
@@ -918,20 +918,20 @@ static void job_completed_txn_abort_locked(Job *job)
         aio_context_acquire(ctx);
         if (!job_is_completed_locked(other_job)) {
             assert(job_cancel_requested_locked(other_job));
-            job_finish_sync(other_job, NULL, NULL);
+            job_finish_sync_locked(other_job, NULL, NULL);
         }
         aio_context_release(ctx);
         job_finalize_single_locked(other_job);
     }
 
     /*
-     * Use job_ref()/job_unref() so we can read the AioContext here
-     * even if the job went away during job_finalize_single_locked().
+     * Use job_ref_locked()/job_unref_locked() so we can read the AioContext
+     * here even if the job went away during job_finalize_single_locked().
      */
     aio_context_acquire(job->aio_context);
-    job_unref(job);
+    job_unref_locked(job);
 
-    job_txn_unref(txn);
+    job_txn_unref_locked(txn);
 }
 
 /* Called with job_mutex held, but releases it temporarly. */
@@ -975,10 +975,10 @@ static void job_do_finalize_locked(Job *job)
     }
 }
 
-void job_finalize(Job *job, Error **errp)
+void job_finalize_locked(Job *job, Error **errp)
 {
     assert(job && job->id);
-    if (job_apply_verb(job, JOB_VERB_FINALIZE, errp)) {
+    if (job_apply_verb_locked(job, JOB_VERB_FINALIZE, errp)) {
         return;
     }
     job_do_finalize_locked(job);
@@ -1052,7 +1052,7 @@ static void job_exit(void *opaque)
     AioContext *ctx;
     JOB_LOCK_GUARD();
 
-    job_ref(job);
+    job_ref_locked(job);
     aio_context_acquire(job->aio_context);
 
     /* This is a lie, we're not quiescent, but still doing the completion
@@ -1072,7 +1072,7 @@ static void job_exit(void *opaque)
      * freeing the job underneath us.
      */
     ctx = job->aio_context;
-    job_unref(job);
+    job_unref_locked(job);
     aio_context_release(ctx);
 }
 
@@ -1113,7 +1113,7 @@ void job_start(Job *job)
     aio_co_enter(job->aio_context, job->co);
 }
 
-void job_cancel(Job *job, bool force)
+void job_cancel_locked(Job *job, bool force)
 {
     if (job->status == JOB_STATUS_CONCLUDED) {
         job_do_dismiss_locked(job);
@@ -1137,28 +1137,28 @@ void job_cancel(Job *job, bool force)
             job_completed_txn_abort_locked(job);
         }
     } else {
-        job_enter_cond(job, NULL);
+        job_enter_cond_locked(job, NULL);
     }
 }
 
-void job_user_cancel(Job *job, bool force, Error **errp)
+void job_user_cancel_locked(Job *job, bool force, Error **errp)
 {
-    if (job_apply_verb(job, JOB_VERB_CANCEL, errp)) {
+    if (job_apply_verb_locked(job, JOB_VERB_CANCEL, errp)) {
         return;
     }
-    job_cancel(job, force);
+    job_cancel_locked(job, force);
 }
 
 /*
- * A wrapper around job_cancel() taking an Error ** parameter so it may be
- * used with job_finish_sync() without the need for (rather nasty) function
- * pointer casts there.
+ * A wrapper around job_cancel_locked() taking an Error ** parameter
+ * so it may be used with job_finish_sync_locked() without the need
+ * for (rather nasty) function pointer casts there.
  *
  * Called with job_mutex held.
  */
 static void job_cancel_err_locked(Job *job, Error **errp)
 {
-    job_cancel(job, false);
+    job_cancel_locked(job, false);
 }
 
 /**
@@ -1167,15 +1167,15 @@ static void job_cancel_err_locked(Job *job, Error **errp)
  */
 static void job_force_cancel_err_locked(Job *job, Error **errp)
 {
-    job_cancel(job, true);
+    job_cancel_locked(job, true);
 }
 
-int job_cancel_sync(Job *job, bool force)
+int job_cancel_sync_locked(Job *job, bool force)
 {
     if (force) {
-        return job_finish_sync(job, &job_force_cancel_err_locked, NULL);
+        return job_finish_sync_locked(job, &job_force_cancel_err_locked, NULL);
     } else {
-        return job_finish_sync(job, &job_cancel_err_locked, NULL);
+        return job_finish_sync_locked(job, &job_cancel_err_locked, NULL);
     }
 }
 
@@ -1185,25 +1185,25 @@ void job_cancel_sync_all(void)
     AioContext *aio_context;
 
     JOB_LOCK_GUARD();
-    while ((job = job_next(NULL))) {
+    while ((job = job_next_locked(NULL))) {
         aio_context = job->aio_context;
         aio_context_acquire(aio_context);
-        job_cancel_sync(job, true);
+        job_cancel_sync_locked(job, true);
         aio_context_release(aio_context);
     }
 }
 
-int job_complete_sync(Job *job, Error **errp)
+int job_complete_sync_locked(Job *job, Error **errp)
 {
-    return job_finish_sync(job, job_complete, errp);
+    return job_finish_sync_locked(job, job_complete_locked, errp);
 }
 
-void job_complete(Job *job, Error **errp)
+void job_complete_locked(Job *job, Error **errp)
 {
     /* Should not be reachable via external interface for internal jobs */
     assert(job->id);
     assert(qemu_in_main_thread());
-    if (job_apply_verb(job, JOB_VERB_COMPLETE, errp)) {
+    if (job_apply_verb_locked(job, JOB_VERB_COMPLETE, errp)) {
         return;
     }
     if (job_cancel_requested_locked(job) || !job->driver->complete) {
@@ -1217,19 +1217,20 @@ void job_complete(Job *job, Error **errp)
     job_lock();
 }
 
-int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp)
+int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
+                           Error **errp)
 {
     Error *local_err = NULL;
     int ret;
 
-    job_ref(job);
+    job_ref_locked(job);
 
     if (finish) {
         finish(job, &local_err);
     }
     if (local_err) {
         error_propagate(errp, local_err);
-        job_unref(job);
+        job_unref_locked(job);
         return -EBUSY;
     }
 
@@ -1240,6 +1241,6 @@ int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp)
 
     ret = (job_is_cancelled_locked(job) && job->ret == 0)
           ? -ECANCELED : job->ret;
-    job_unref(job);
+    job_unref_locked(job);
     return ret;
 }
diff --git a/qemu-img.c b/qemu-img.c
index 320d82b42a..315c9c2a31 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -907,7 +907,7 @@ static void run_block_job(BlockJob *job, Error **errp)
 
     aio_context_acquire(aio_context);
     WITH_JOB_LOCK_GUARD() {
-        job_ref(&job->job);
+        job_ref_locked(&job->job);
         do {
             float progress = 0.0f;
             job_unlock();
@@ -924,11 +924,11 @@ static void run_block_job(BlockJob *job, Error **errp)
                  !job_is_completed_locked(&job->job));
 
         if (!job_is_completed_locked(&job->job)) {
-            ret = job_complete_sync(&job->job, errp);
+            ret = job_complete_sync_locked(&job->job, errp);
         } else {
             ret = job->job.ret;
         }
-        job_unref(&job->job);
+        job_unref_locked(&job->job);
     }
     aio_context_release(aio_context);
 
diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index 181458eecb..0db056ea63 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -1018,7 +1018,7 @@ static void test_blockjob_common_drain_node(enum drain_type drain_type,
 
     aio_context_acquire(ctx);
     WITH_JOB_LOCK_GUARD() {
-        ret = job_complete_sync(&job->job, &error_abort);
+        ret = job_complete_sync_locked(&job->job, &error_abort);
     }
     g_assert_cmpint(ret, ==, (result == TEST_JOB_SUCCESS ? 0 : -EIO));
 
diff --git a/tests/unit/test-block-iothread.c b/tests/unit/test-block-iothread.c
index 9866262f79..89e7f0fffb 100644
--- a/tests/unit/test-block-iothread.c
+++ b/tests/unit/test-block-iothread.c
@@ -457,7 +457,7 @@ static void test_attach_blockjob(void)
 
     aio_context_acquire(ctx);
     WITH_JOB_LOCK_GUARD() {
-        job_complete_sync(&tjob->common.job, &error_abort);
+        job_complete_sync_locked(&tjob->common.job, &error_abort);
     }
     blk_set_aio_context(blk, qemu_get_aio_context(), &error_abort);
     aio_context_release(ctx);
@@ -633,7 +633,7 @@ static void test_propagate_mirror(void)
                  false, "filter_node", MIRROR_COPY_MODE_BACKGROUND,
                  &error_abort);
     WITH_JOB_LOCK_GUARD() {
-        job = job_get("job0");
+        job = job_get_locked("job0");
     }
     filter = bdrv_find_node("filter_node");
 
diff --git a/tests/unit/test-blockjob-txn.c b/tests/unit/test-blockjob-txn.c
index 0355e54001..8dc1eaefc8 100644
--- a/tests/unit/test-blockjob-txn.c
+++ b/tests/unit/test-blockjob-txn.c
@@ -118,7 +118,7 @@ static void test_single_job(int expected)
 
     WITH_JOB_LOCK_GUARD() {
         if (expected == -ECANCELED) {
-            job_cancel(&job->job, false);
+            job_cancel_locked(&job->job, false);
         }
     }
 
@@ -128,7 +128,7 @@ static void test_single_job(int expected)
     g_assert_cmpint(result, ==, expected);
 
     WITH_JOB_LOCK_GUARD() {
-        job_txn_unref(txn);
+        job_txn_unref_locked(txn);
     }
 }
 
@@ -165,13 +165,13 @@ static void test_pair_jobs(int expected1, int expected2)
      * use-after-free bugs as possible.
      */
     WITH_JOB_LOCK_GUARD() {
-        job_txn_unref(txn);
+        job_txn_unref_locked(txn);
 
         if (expected1 == -ECANCELED) {
-            job_cancel(&job1->job, false);
+            job_cancel_locked(&job1->job, false);
         }
         if (expected2 == -ECANCELED) {
-            job_cancel(&job2->job, false);
+            job_cancel_locked(&job2->job, false);
         }
     }
 
@@ -226,7 +226,7 @@ static void test_pair_jobs_fail_cancel_race(void)
     job_start(&job2->job);
 
     WITH_JOB_LOCK_GUARD() {
-        job_cancel(&job1->job, false);
+        job_cancel_locked(&job1->job, false);
     }
 
     /* Now make job2 finish before the main loop kicks jobs.  This simulates
@@ -243,7 +243,7 @@ static void test_pair_jobs_fail_cancel_race(void)
     g_assert_cmpint(result2, ==, -ECANCELED);
 
     WITH_JOB_LOCK_GUARD() {
-        job_txn_unref(txn);
+        job_txn_unref_locked(txn);
     }
 }
 
diff --git a/tests/unit/test-blockjob.c b/tests/unit/test-blockjob.c
index ab7958dad5..8280b1e0c9 100644
--- a/tests/unit/test-blockjob.c
+++ b/tests/unit/test-blockjob.c
@@ -212,7 +212,7 @@ static CancelJob *create_common(Job **pjob)
                   JOB_MANUAL_FINALIZE | JOB_MANUAL_DISMISS);
     job = &bjob->job;
     WITH_JOB_LOCK_GUARD() {
-        job_ref(job);
+        job_ref_locked(job);
         assert(job->status == JOB_STATUS_CREATED);
     }
 
@@ -234,13 +234,13 @@ static void cancel_common(CancelJob *s)
     aio_context_acquire(ctx);
 
     WITH_JOB_LOCK_GUARD() {
-        job_cancel_sync(&job->job, true);
+        job_cancel_sync_locked(&job->job, true);
         if (sts != JOB_STATUS_CREATED && sts != JOB_STATUS_CONCLUDED) {
             Job *dummy = &job->job;
-            job_dismiss(&dummy, &error_abort);
+            job_dismiss_locked(&dummy, &error_abort);
         }
         assert(job->job.status == JOB_STATUS_NULL);
-        job_unref(&job->job);
+        job_unref_locked(&job->job);
     }
     destroy_blk(blk);
 
@@ -288,7 +288,7 @@ static void test_cancel_paused(void)
     assert(job->status == JOB_STATUS_RUNNING);
 
     WITH_JOB_LOCK_GUARD() {
-        job_user_pause(job, &error_abort);
+        job_user_pause_locked(job, &error_abort);
     }
     job_enter(job);
     assert(job->status == JOB_STATUS_PAUSED);
@@ -336,7 +336,7 @@ static void test_cancel_standby(void)
     assert(job->status == JOB_STATUS_READY);
 
     WITH_JOB_LOCK_GUARD() {
-        job_user_pause(job, &error_abort);
+        job_user_pause_locked(job, &error_abort);
     }
     job_enter(job);
     assert(job->status == JOB_STATUS_STANDBY);
@@ -363,7 +363,7 @@ static void test_cancel_pending(void)
     assert(job->status == JOB_STATUS_READY);
 
     WITH_JOB_LOCK_GUARD() {
-        job_complete(job, &error_abort);
+        job_complete_locked(job, &error_abort);
     }
     job_enter(job);
     while (!job->deferred_to_main_loop) {
@@ -395,7 +395,7 @@ static void test_cancel_concluded(void)
     assert(job->status == JOB_STATUS_READY);
 
     WITH_JOB_LOCK_GUARD() {
-        job_complete(job, &error_abort);
+        job_complete_locked(job, &error_abort);
     }
     job_enter(job);
     while (!job->deferred_to_main_loop) {
@@ -407,7 +407,7 @@ static void test_cancel_concluded(void)
 
     aio_context_acquire(job->aio_context);
     WITH_JOB_LOCK_GUARD() {
-        job_finalize(job, &error_abort);
+        job_finalize_locked(job, &error_abort);
     }
     aio_context_release(job->aio_context);
     assert(job->status == JOB_STATUS_CONCLUDED);
@@ -456,7 +456,7 @@ static const BlockJobDriver test_yielding_driver = {
 };
 
 /*
- * Test that job_complete() works even on jobs that are in a paused
+ * Test that job_complete_locked() works even on jobs that are in a paused
  * state (i.e., STANDBY).
  *
  * To do this, run YieldingJob in an IO thread, get it into the READY
@@ -464,7 +464,7 @@ static const BlockJobDriver test_yielding_driver = {
  * acquire the context so the job will not be entered and will thus
  * remain on STANDBY.
  *
- * job_complete() should still work without error.
+ * job_complete_locked() should still work without error.
  *
  * Note that on the QMP interface, it is impossible to lock an IO
  * thread before a drained section ends.  In practice, the
@@ -526,16 +526,16 @@ static void test_complete_in_standby(void)
         assert(job->status == JOB_STATUS_STANDBY);
 
         /* Even though the job is on standby, this should work */
-        job_complete(job, &error_abort);
+        job_complete_locked(job, &error_abort);
 
         /* The test is done now, clean up. */
-        job_finish_sync(job, NULL, &error_abort);
+        job_finish_sync_locked(job, NULL, &error_abort);
         assert(job->status == JOB_STATUS_PENDING);
 
-        job_finalize(job, &error_abort);
+        job_finalize_locked(job, &error_abort);
         assert(job->status == JOB_STATUS_CONCLUDED);
 
-        job_dismiss(&job, &error_abort);
+        job_dismiss_locked(&job, &error_abort);
     }
 
     destroy_blk(blk);
-- 
2.31.1

[PATCH v5 14/20] block_job: rename block_job functions called with job_mutex held

[Emanuele Giuseppe Esposito]

Just as for the job API, rename block_job functions that are
always called under job lock.

No functional change intended.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block.c                  |  3 ++-
 block/backup.c           |  4 ++--
 blockdev.c               | 12 +++++++-----
 blockjob.c               | 39 ++++++++++++++++++++++-----------------
 include/block/blockjob.h | 29 ++++++++++++++++++-----------
 monitor/qmp-cmds.c       |  5 +++--
 qemu-img.c               |  2 +-
 7 files changed, 55 insertions(+), 39 deletions(-)

diff --git a/block.c b/block.c
index 1edb59aaae..e42a99d2af 100644
--- a/block.c
+++ b/block.c
@@ -6148,7 +6148,8 @@ XDbgBlockGraph *bdrv_get_xdbg_block_graph(Error **errp)
     }
 
     WITH_JOB_LOCK_GUARD() {
-        for (job = block_job_next(NULL); job; job = block_job_next(job)) {
+        for (job = block_job_next_locked(NULL); job;
+             job = block_job_next_locked(job)) {
             GSList *el;
 
             xdbg_graph_add_node(gr, job, X_DBG_BLOCK_GRAPH_NODE_TYPE_BLOCK_JOB,
diff --git a/block/backup.c b/block/backup.c
index c53041772c..c29f3c1ae8 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -316,8 +316,8 @@ static void coroutine_fn backup_set_speed(BlockJob *job, int64_t speed)
     BackupBlockJob *s = container_of(job, BackupBlockJob, common);
 
     /*
-     * block_job_set_speed() is called first from block_job_create(), when we
-     * don't yet have s->bcs.
+     * block_job_set_speed_locked() is called first from block_job_create(),
+     * when we don't yet have s->bcs.
      */
     if (s->bcs) {
         block_copy_set_speed(s->bcs, speed);
diff --git a/blockdev.c b/blockdev.c
index 4bcb09ad9e..fd436024b4 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -152,7 +152,8 @@ void blockdev_mark_auto_del(BlockBackend *blk)
 
     JOB_LOCK_GUARD();
 
-    for (job = block_job_next(NULL); job; job = block_job_next(job)) {
+    for (job = block_job_next_locked(NULL); job;
+         job = block_job_next_locked(job)) {
         if (block_job_has_bdrv(job, blk_bs(blk))) {
             AioContext *aio_context = job->job.aio_context;
             aio_context_acquire(aio_context);
@@ -3325,7 +3326,7 @@ static BlockJob *find_block_job(const char *id, AioContext **aio_context,
     *aio_context = NULL;
     job_lock();
 
-    job = block_job_get(id);
+    job = block_job_get_locked(id);
 
     if (!job) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
@@ -3349,7 +3350,7 @@ void qmp_block_job_set_speed(const char *device, int64_t speed, Error **errp)
         return;
     }
 
-    block_job_set_speed(job, speed, errp);
+    block_job_set_speed_locked(job, speed, errp);
     aio_context_release(aio_context);
     job_unlock();
 }
@@ -3734,13 +3735,14 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
 
     JOB_LOCK_GUARD();
 
-    for (job = block_job_next(NULL); job; job = block_job_next(job)) {
+    for (job = block_job_next_locked(NULL); job;
+         job = block_job_next_locked(job)) {
         BlockJobInfo *value;
 
         if (block_job_is_internal(job)) {
             continue;
         }
-        value = block_job_query(job, errp);
+        value = block_job_query_locked(job, errp);
         if (!value) {
             qapi_free_BlockJobInfoList(head);
             return NULL;
diff --git a/blockjob.c b/blockjob.c
index c9b811e911..24eac9d0e3 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -59,7 +59,7 @@ static bool is_block_job(Job *job)
            job_type(job) == JOB_TYPE_STREAM;
 }
 
-BlockJob *block_job_next(BlockJob *bjob)
+BlockJob *block_job_next_locked(BlockJob *bjob)
 {
     Job *job = bjob ? &bjob->job : NULL;
     assert(qemu_in_main_thread());
@@ -71,7 +71,7 @@ BlockJob *block_job_next(BlockJob *bjob)
     return job ? container_of(job, BlockJob, job) : NULL;
 }
 
-BlockJob *block_job_get(const char *id)
+BlockJob *block_job_get_locked(const char *id)
 {
     Job *job = job_get_locked(id);
     assert(qemu_in_main_thread());
@@ -256,7 +256,8 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
     return 0;
 }
 
-static void block_job_on_idle(Notifier *n, void *opaque)
+/* Called with job_mutex lock held. */
+static void block_job_on_idle_locked(Notifier *n, void *opaque)
 {
     /*
      * we can't kick with job_mutex held, but we also want
@@ -283,7 +284,7 @@ static bool job_timer_pending(Job *job)
     return timer_pending(&job->sleep_timer);
 }
 
-bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
+bool block_job_set_speed_locked(BlockJob *job, int64_t speed, Error **errp)
 {
     const BlockJobDriver *drv = block_job_driver(job);
     int64_t old_speed = job->speed;
@@ -324,7 +325,7 @@ int64_t block_job_ratelimit_get_delay(BlockJob *job, uint64_t n)
     return ratelimit_calculate_delay(&job->limit, n);
 }
 
-BlockJobInfo *block_job_query(BlockJob *job, Error **errp)
+BlockJobInfo *block_job_query_locked(BlockJob *job, Error **errp)
 {
     BlockJobInfo *info;
     uint64_t progress_current, progress_total;
@@ -369,7 +370,8 @@ static void block_job_iostatus_set_err(BlockJob *job, int error)
     }
 }
 
-static void block_job_event_cancelled(Notifier *n, void *opaque)
+/* Called with job_mutex lock held. */
+static void block_job_event_cancelled_locked(Notifier *n, void *opaque)
 {
     BlockJob *job = opaque;
     uint64_t progress_current, progress_total;
@@ -388,7 +390,8 @@ static void block_job_event_cancelled(Notifier *n, void *opaque)
                                         job->speed);
 }
 
-static void block_job_event_completed(Notifier *n, void *opaque)
+/* Called with job_mutex lock held. */
+static void block_job_event_completed_locked(Notifier *n, void *opaque)
 {
     BlockJob *job = opaque;
     const char *msg = NULL;
@@ -414,7 +417,8 @@ static void block_job_event_completed(Notifier *n, void *opaque)
                                         msg);
 }
 
-static void block_job_event_pending(Notifier *n, void *opaque)
+/* Called with job_mutex lock held. */
+static void block_job_event_pending_locked(Notifier *n, void *opaque)
 {
     BlockJob *job = opaque;
 
@@ -426,7 +430,8 @@ static void block_job_event_pending(Notifier *n, void *opaque)
                                       job->job.id);
 }
 
-static void block_job_event_ready(Notifier *n, void *opaque)
+/* Called with job_mutex lock held. */
+static void block_job_event_ready_locked(Notifier *n, void *opaque)
 {
     BlockJob *job = opaque;
     uint64_t progress_current, progress_total;
@@ -477,11 +482,11 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
 
     ratelimit_init(&job->limit);
 
-    job->finalize_cancelled_notifier.notify = block_job_event_cancelled;
-    job->finalize_completed_notifier.notify = block_job_event_completed;
-    job->pending_notifier.notify = block_job_event_pending;
-    job->ready_notifier.notify = block_job_event_ready;
-    job->idle_notifier.notify = block_job_on_idle;
+    job->finalize_cancelled_notifier.notify = block_job_event_cancelled_locked;
+    job->finalize_completed_notifier.notify = block_job_event_completed_locked;
+    job->pending_notifier.notify = block_job_event_pending_locked;
+    job->ready_notifier.notify = block_job_event_ready_locked;
+    job->idle_notifier.notify = block_job_on_idle_locked;
 
     WITH_JOB_LOCK_GUARD() {
         notifier_list_add(&job->job.on_finalize_cancelled,
@@ -504,7 +509,7 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
     bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
 
     WITH_JOB_LOCK_GUARD() {
-        ret = block_job_set_speed(job, speed, errp);
+        ret = block_job_set_speed_locked(job, speed, errp);
     }
     if (!ret) {
         goto fail;
@@ -517,7 +522,7 @@ fail:
     return NULL;
 }
 
-void block_job_iostatus_reset(BlockJob *job)
+void block_job_iostatus_reset_locked(BlockJob *job)
 {
     assert(qemu_in_main_thread());
     if (job->iostatus == BLOCK_DEVICE_IO_STATUS_OK) {
@@ -532,7 +537,7 @@ void block_job_user_resume(Job *job)
     BlockJob *bjob = container_of(job, BlockJob, job);
     assert(qemu_in_main_thread());
     WITH_JOB_LOCK_GUARD() {
-        block_job_iostatus_reset(bjob);
+        block_job_iostatus_reset_locked(bjob);
     }
 }
 
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 6525e16fd5..000f5a1d21 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -46,7 +46,7 @@ typedef struct BlockJob {
     /** Status that is published by the query-block-jobs QMP API */
     BlockDeviceIoStatus iostatus;
 
-    /** Speed that was set with @block_job_set_speed.  */
+    /** Speed that was set with @block_job_set_speed_locked.  */
     int64_t speed;
 
     /** Rate limiting data structure for implementing @speed. */
@@ -82,25 +82,27 @@ typedef struct BlockJob {
  */
 
 /**
- * block_job_next:
+ * block_job_next_locked:
  * @job: A block job, or %NULL.
  *
  * Get the next element from the list of block jobs after @job, or the
  * first one if @job is %NULL.
  *
  * Returns the requested job, or %NULL if there are no more jobs left.
+ * Called with job_mutex lock held.
  */
-BlockJob *block_job_next(BlockJob *job);
+BlockJob *block_job_next_locked(BlockJob *job);
 
 /**
- * block_job_get:
+ * block_job_get_locked:
  * @id: The id of the block job.
  *
  * Get the block job identified by @id (which must not be %NULL).
  *
  * Returns the requested job, or %NULL if it doesn't exist.
+ * Called with job_mutex lock held.
  */
-BlockJob *block_job_get(const char *id);
+BlockJob *block_job_get_locked(const char *id);
 
 /**
  * block_job_add_bdrv:
@@ -135,32 +137,37 @@ void block_job_remove_all_bdrv(BlockJob *job);
 bool block_job_has_bdrv(BlockJob *job, BlockDriverState *bs);
 
 /**
- * block_job_set_speed:
+ * block_job_set_speed_locked:
  * @job: The job to set the speed for.
  * @speed: The new value
  * @errp: Error object.
  *
  * Set a rate-limiting parameter for the job; the actual meaning may
  * vary depending on the job type.
+ *
+ * Called with job_mutex lock held. May temporarly release the lock.
  */
-bool block_job_set_speed(BlockJob *job, int64_t speed, Error **errp);
+bool block_job_set_speed_locked(BlockJob *job, int64_t speed, Error **errp);
 
 /**
- * block_job_query:
+ * block_job_query_locked:
  * @job: The job to get information about.
  *
  * Return information about a job.
+ * Called with job_mutex lock held.
  */
-BlockJobInfo *block_job_query(BlockJob *job, Error **errp);
+BlockJobInfo *block_job_query_locked(BlockJob *job, Error **errp);
 
 /**
- * block_job_iostatus_reset:
+ * block_job_iostatus_reset_locked:
  * @job: The job whose I/O status should be reset.
  *
  * Reset I/O status on @job and on BlockDriverState objects it uses,
  * other than job->blk.
+ *
+ * Called with job_mutex lock held.
  */
-void block_job_iostatus_reset(BlockJob *job);
+void block_job_iostatus_reset_locked(BlockJob *job);
 
 /*
  * block_job_get_aio_context:
diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
index 97a16efcdc..ff78110d76 100644
--- a/monitor/qmp-cmds.c
+++ b/monitor/qmp-cmds.c
@@ -135,8 +135,9 @@ void qmp_cont(Error **errp)
     }
 
     WITH_JOB_LOCK_GUARD() {
-        for (job = block_job_next(NULL); job; job = block_job_next(job)) {
-            block_job_iostatus_reset(job);
+        for (job = block_job_next_locked(NULL); job;
+             job = block_job_next_locked(job)) {
+            block_job_iostatus_reset_locked(job);
         }
     }
 
diff --git a/qemu-img.c b/qemu-img.c
index 315c9c2a31..222c9fdf5c 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1083,7 +1083,7 @@ static int img_commit(int argc, char **argv)
     }
 
     WITH_JOB_LOCK_GUARD() {
-        job = block_job_get("commit");
+        job = block_job_get_locked("commit");
     }
     assert(job);
     run_block_job(job, &local_err);
-- 
2.31.1

[PATCH v5 15/20] job.h: define unlocked functions

[Emanuele Giuseppe Esposito]

All these functions assume that the lock is not held, and acquire
it internally.

These functions will be useful when job_lock is globally applied,
as they will allow callers to access the job struct fields
without worrying about the job lock.

Update also the comments in blockjob.c (and move them in job.c).

Note: at this stage, job_{lock/unlock} and job lock guard macros
are *nop*.

No functional change intended.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 blockjob.c         | 20 --------------------
 include/qemu/job.h | 37 ++++++++++++++++++++++++++++++++++---
 job.c              | 16 ++++++++++++++++
 3 files changed, 50 insertions(+), 23 deletions(-)

diff --git a/blockjob.c b/blockjob.c
index 24eac9d0e3..04d868f020 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -36,21 +36,6 @@
 #include "qemu/main-loop.h"
 #include "qemu/timer.h"
 
-/*
- * The block job API is composed of two categories of functions.
- *
- * The first includes functions used by the monitor.  The monitor is
- * peculiar in that it accesses the block job list with block_job_get, and
- * therefore needs consistency across block_job_get and the actual operation
- * (e.g. block_job_set_speed).  The consistency is achieved with
- * aio_context_acquire/release.  These functions are declared in blockjob.h.
- *
- * The second includes functions used by the block job drivers and sometimes
- * by the core block layer.  These do not care about locking, because the
- * whole coroutine runs under the AioContext lock, and are declared in
- * blockjob_int.h.
- */
-
 static bool is_block_job(Job *job)
 {
     return job_type(job) == JOB_TYPE_BACKUP ||
@@ -451,11 +436,6 @@ static void block_job_event_ready_locked(Notifier *n, void *opaque)
 }
 
 
-/*
- * API for block job drivers and the block layer.  These functions are
- * declared in blockjob_int.h.
- */
-
 void *block_job_create(const char *job_id, const BlockJobDriver *driver,
                        JobTxn *txn, BlockDriverState *bs, uint64_t perm,
                        uint64_t shared_perm, int64_t speed, int flags,
diff --git a/include/qemu/job.h b/include/qemu/job.h
index dfd2586e63..dfbf2ea501 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -360,6 +360,7 @@ void job_txn_unref_locked(JobTxn *txn);
 
 /**
  * Create a new long-running job and return it.
+ * Called with job_mutex *not* held.
  *
  * @job_id: The id of the newly-created job, or %NULL for internal jobs
  * @driver: The class object for the newly-created job.
@@ -395,6 +396,8 @@ void job_unref_locked(Job *job);
  * @done: How much progress the job made since the last call
  *
  * Updates the progress counter of the job.
+ *
+ * Progress API is thread safe.
  */
 void job_progress_update(Job *job, uint64_t done);
 
@@ -405,6 +408,8 @@ void job_progress_update(Job *job, uint64_t done);
  *
  * Sets the expected end value of the progress counter of a job so that a
  * completion percentage can be calculated when the progress is updated.
+ *
+ * Progress API is thread safe.
  */
 void job_progress_set_remaining(Job *job, uint64_t remaining);
 
@@ -420,6 +425,8 @@ void job_progress_set_remaining(Job *job, uint64_t remaining);
  * length before, and job_progress_update() afterwards.
  * (So the operation acts as a parenthesis in regards to the main job
  * operation running in background.)
+ *
+ * Progress API is thread safe.
  */
 void job_progress_increase_remaining(Job *job, uint64_t delta);
 
@@ -437,13 +444,17 @@ void job_enter_cond_locked(Job *job, bool(*fn)(Job *job));
  *
  * Begins execution of a job.
  * Takes ownership of one reference to the job object.
+ *
+ * Called with job_mutex *not* held.
  */
 void job_start(Job *job);
 
 /**
  * @job: The job to enter.
+ * Called with job_mutex *not* held.
  *
  * Continue the specified job by entering the coroutine.
+ * Called with job_mutex lock *not* held.
  */
 void job_enter(Job *job);
 
@@ -452,6 +463,9 @@ void job_enter(Job *job);
  *
  * Pause now if job_pause_locked() has been called. Jobs that perform lots of
  * I/O must call this between requests so that the job can be paused.
+ *
+ * Called with job_mutex *not* held (we don't want the coroutine
+ * to yield with the lock held!).
  */
 void coroutine_fn job_pause_point(Job *job);
 
@@ -459,6 +473,8 @@ void coroutine_fn job_pause_point(Job *job);
  * @job: The job that calls the function.
  *
  * Yield the job coroutine.
+ * Called with job_mutex *not* held (we don't want the coroutine
+ * to yield with the lock held!).
  */
 void job_yield(Job *job);
 
@@ -469,6 +485,9 @@ void job_yield(Job *job);
  * Put the job to sleep (assuming that it wasn't canceled) for @ns
  * %QEMU_CLOCK_REALTIME nanoseconds.  Canceling the job will immediately
  * interrupt the wait.
+ *
+ * Called with job_mutex *not* held (we don't want the coroutine
+ * to yield with the lock held!).
  */
 void coroutine_fn job_sleep_ns(Job *job, int64_t ns);
 
@@ -580,10 +599,16 @@ Job *job_get_locked(const char *id);
  */
 int job_apply_verb_locked(Job *job, JobVerb verb, Error **errp);
 
-/** The @job could not be started, free it. */
+/**
+ * The @job could not be started, free it.
+ * Called with job_mutex *not* held.
+ */
 void job_early_fail(Job *job);
 
-/** Moves the @job from RUNNING to READY */
+/**
+ * Moves the @job from RUNNING to READY.
+ * Called with job_mutex *not* held.
+ */
 void job_transition_to_ready(Job *job);
 
 /**
@@ -622,7 +647,13 @@ void job_user_cancel_locked(Job *job, bool force, Error **errp);
  */
 int job_cancel_sync_locked(Job *job, bool force);
 
-/** Synchronously force-cancels all jobs using job_cancel_sync_locked(). */
+/**
+ * Synchronously force-cancels all jobs using job_cancel_sync_locked().
+ *
+ * Called with job_lock *not* held, unlike most other APIs consumed
+ * by the monitor! This is primarly to avoid adding unnecessary lock-unlock
+ * patterns in the caller.
+ */
 void job_cancel_sync_all(void);
 
 /**
diff --git a/job.c b/job.c
index 0ab25cb37e..83cc9f52bd 100644
--- a/job.c
+++ b/job.c
@@ -32,12 +32,27 @@
 #include "trace/trace-root.h"
 #include "qapi/qapi-events-job.h"
 
+/*
+ * The job API is composed of two categories of functions.
+ *
+ * The first includes functions used by the monitor.  The monitor is
+ * peculiar in that it accesses the block job list with job_get, and
+ * therefore needs consistency across job_get and the actual operation
+ * (e.g. job_user_cancel). To achieve this consistency, the caller
+ * calls job_lock/job_unlock itself around the whole operation.
+ *
+ *
+ * The second includes functions used by the block job drivers and sometimes
+ * by the core block layer. These delegate the locking to the callee instead.
+ */
+
 /*
  * job_mutex protects the jobs list, but also makes the
  * struct job fields thread-safe.
  */
 QemuMutex job_mutex;
 
+/* Protected by job_mutex */
 static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
 
 /* Job State Transition Table */
@@ -339,6 +354,7 @@ Job *job_get_locked(const char *id)
     return NULL;
 }
 
+/* Called with job_mutex *not* held. */
 static void job_sleep_timer_cb(void *opaque)
 {
     Job *job = opaque;
-- 
2.31.1

[PATCH v5 16/20] commit and mirror: create new nodes using bdrv_get_aio_context, and not the job aiocontext

[Emanuele Giuseppe Esposito]

We are always using the given bs AioContext, so there is no need
to take the job ones (which is identical anyways).
This also reduces the point we need to check when protecting
job.aio_context field.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/commit.c | 4 ++--
 block/mirror.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/commit.c b/block/commit.c
index 2883a3ba52..3ea460fe4a 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -369,7 +369,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
         goto fail;
     }
 
-    s->base = blk_new(s->common.job.aio_context,
+    s->base = blk_new(bdrv_get_aio_context(bs),
                       base_perms,
                       BLK_PERM_CONSISTENT_READ
                       | BLK_PERM_WRITE_UNCHANGED);
@@ -381,7 +381,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     s->base_bs = base;
 
     /* Required permissions are already taken with block_job_add_bdrv() */
-    s->top = blk_new(s->common.job.aio_context, 0, BLK_PERM_ALL);
+    s->top = blk_new(bdrv_get_aio_context(bs), 0, BLK_PERM_ALL);
     ret = blk_insert_bs(s->top, top, errp);
     if (ret < 0) {
         goto fail;
diff --git a/block/mirror.c b/block/mirror.c
index 0a3eb712e6..28d137407c 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1727,7 +1727,7 @@ static BlockJob *mirror_start_job(
         goto fail;
     }
 
-    s->target = blk_new(s->common.job.aio_context,
+    s->target = blk_new(bdrv_get_aio_context(bs),
                         target_perms, target_shared_perms);
     ret = blk_insert_bs(s->target, target, errp);
     if (ret < 0) {
-- 
2.31.1

Re: [PATCH v5 16/20] commit and mirror: create new nodes using bdrv_get_aio_context, and not the job aiocontext

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 528 bytes --]

On Tue, Feb 08, 2022 at 09:35:09AM -0500, Emanuele Giuseppe Esposito wrote:
> We are always using the given bs AioContext, so there is no need
> to take the job ones (which is identical anyways).
> This also reduces the point we need to check when protecting
> job.aio_context field.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  block/commit.c | 4 ++--
>  block/mirror.c | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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[PATCH v5 17/20] job: detect change of aiocontext within job coroutine

[Emanuele Giuseppe Esposito]

From: Paolo Bonzini <pbonzini@redhat.com>

We want to make sure access of job->aio_context is always done
under either BQL or job_mutex. The problem is that using
aio_co_enter(job->aiocontext, job->co) in job_start and job_enter_cond
makes the coroutine immediately resume, so we can't hold the job lock.
And caching it is not safe either, as it might change.

job_start is under BQL, so it can freely read job->aiocontext, but
job_enter_cond is not. In order to fix this, use aio_co_wake():
the advantage is that it won't use job->aiocontext, but the
main disadvantage is that it won't be able to detect a change of
job AioContext.

Calling bdrv_try_set_aio_context() will issue the following calls
(simplified):
* in terms of  bdrv callbacks:
  .drained_begin -> .set_aio_context -> .drained_end
* in terms of child_job functions:
  child_job_drained_begin -> child_job_set_aio_context -> child_job_drained_end
* in terms of job functions:
  job_pause_locked -> job_set_aio_context -> job_resume_locked

We can see that after setting the new aio_context, job_resume_locked
calls again job_enter_cond, which then invokes aio_co_wake(). But
while job->aiocontext has been set in job_set_aio_context,
job->co->ctx has not changed, so the coroutine would be entering in
the wrong aiocontext.

Using aio_co_schedule in job_resume_locked() might seem as a valid
alternative, but the problem is that the bh resuming the coroutine
is not scheduled immediately, and if in the meanwhile another
bdrv_try_set_aio_context() is run (see test_propagate_mirror() in
test-block-iothread.c), we would have the first schedule in the
wrong aiocontext, and the second set of drains won't even manage
to schedule the coroutine, as job->busy would still be true from
the previous job_resume_locked().

The solution is to stick with aio_co_wake(), but then detect every time
the coroutine resumes back from yielding if job->aio_context
has changed. If so, we can reschedule it to the new context.

Check for the aiocontext change in job_do_yield_locked because:
1) aio_co_reschedule_self requires to be in the running coroutine
2) since child_job_set_aio_context allows changing the aiocontext only
   while the job is paused, this is the exact place where the coroutine
   resumes, before running JobDriver's code.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 job.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/job.c b/job.c
index 83cc9f52bd..f05850a337 100644
--- a/job.c
+++ b/job.c
@@ -529,11 +529,12 @@ void job_enter_cond_locked(Job *job, bool(*fn)(Job *job))
         return;
     }
 
-    assert(!job->deferred_to_main_loop);
     timer_del(&job->sleep_timer);
     job->busy = true;
     real_job_unlock();
-    aio_co_enter(job->aio_context, job->co);
+    job_unlock();
+    aio_co_wake(job->co);
+    job_lock();
 }
 
 void job_enter(Job *job)
@@ -554,6 +555,8 @@ void job_enter(Job *job)
  */
 static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns)
 {
+    AioContext *next_aio_context;
+
     real_job_lock();
     if (ns != -1) {
         timer_mod(&job->sleep_timer, ns);
@@ -565,6 +568,20 @@ static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns)
     qemu_coroutine_yield();
     job_lock();
 
+    next_aio_context = job->aio_context;
+    /*
+     * Coroutine has resumed, but in the meanwhile the job AioContext
+     * might have changed via bdrv_try_set_aio_context(), so we need to move
+     * the coroutine too in the new aiocontext.
+     */
+    while (qemu_get_current_aio_context() != next_aio_context) {
+        job_unlock();
+        aio_co_reschedule_self(next_aio_context);
+        job_lock();
+        next_aio_context = job->aio_context;
+    }
+
+
     /* Set by job_enter_cond_locked() before re-entering the coroutine.  */
     assert(job->busy);
 }
@@ -666,7 +683,6 @@ void job_resume_locked(Job *job)
     if (job->pause_count) {
         return;
     }
-
     /* kick only if no timer is pending */
     job_enter_cond_locked(job, job_timer_not_pending_locked);
 }
@@ -1117,6 +1133,8 @@ static void coroutine_fn job_co_entry(void *opaque)
 
 void job_start(Job *job)
 {
+    assert(qemu_in_main_thread());
+
     WITH_JOB_LOCK_GUARD() {
         assert(job && !job_started(job) && job->paused &&
             job->driver && job->driver->run);
-- 
2.31.1

Re: [PATCH v5 17/20] job: detect change of aiocontext within job coroutine

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 2725 bytes --]

On Tue, Feb 08, 2022 at 09:35:10AM -0500, Emanuele Giuseppe Esposito wrote:
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> We want to make sure access of job->aio_context is always done
> under either BQL or job_mutex. The problem is that using
> aio_co_enter(job->aiocontext, job->co) in job_start and job_enter_cond
> makes the coroutine immediately resume, so we can't hold the job lock.
> And caching it is not safe either, as it might change.
> 
> job_start is under BQL, so it can freely read job->aiocontext, but
> job_enter_cond is not. In order to fix this, use aio_co_wake():
> the advantage is that it won't use job->aiocontext, but the
> main disadvantage is that it won't be able to detect a change of
> job AioContext.
> 
> Calling bdrv_try_set_aio_context() will issue the following calls
> (simplified):
> * in terms of  bdrv callbacks:
>   .drained_begin -> .set_aio_context -> .drained_end
> * in terms of child_job functions:
>   child_job_drained_begin -> child_job_set_aio_context -> child_job_drained_end
> * in terms of job functions:
>   job_pause_locked -> job_set_aio_context -> job_resume_locked
> 
> We can see that after setting the new aio_context, job_resume_locked
> calls again job_enter_cond, which then invokes aio_co_wake(). But
> while job->aiocontext has been set in job_set_aio_context,
> job->co->ctx has not changed, so the coroutine would be entering in
> the wrong aiocontext.
> 
> Using aio_co_schedule in job_resume_locked() might seem as a valid
> alternative, but the problem is that the bh resuming the coroutine
> is not scheduled immediately, and if in the meanwhile another
> bdrv_try_set_aio_context() is run (see test_propagate_mirror() in
> test-block-iothread.c), we would have the first schedule in the
> wrong aiocontext, and the second set of drains won't even manage
> to schedule the coroutine, as job->busy would still be true from
> the previous job_resume_locked().
> 
> The solution is to stick with aio_co_wake(), but then detect every time
> the coroutine resumes back from yielding if job->aio_context
> has changed. If so, we can reschedule it to the new context.
> 
> Check for the aiocontext change in job_do_yield_locked because:
> 1) aio_co_reschedule_self requires to be in the running coroutine
> 2) since child_job_set_aio_context allows changing the aiocontext only
>    while the job is paused, this is the exact place where the coroutine
>    resumes, before running JobDriver's code.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  job.c | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

[-- Attachment #2: signature.asc --]
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[PATCH v5 18/20] jobs: protect job.aio_context with BQL and job_mutex

[Emanuele Giuseppe Esposito]

In order to make it thread safe, implement a "fake rwlock",
where we allow reads under BQL *or* job_mutex held, but
writes only under BQL *and* job_mutex.

The only write we have is in child_job_set_aio_ctx, which always
happens under drain (so the job is paused).
For this reason, introduce job_set_aio_context and make sure that
the context is set under BQL, job_mutex and drain.
Also make sure all other places where the aiocontext is read
are protected.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/replication.c |  2 +-
 blockjob.c          |  3 ++-
 include/qemu/job.h  | 19 ++++++++++++++++++-
 job.c               | 12 ++++++++++++
 4 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/block/replication.c b/block/replication.c
index 50ea778937..68018948b9 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -148,8 +148,8 @@ static void replication_close(BlockDriverState *bs)
     }
     if (s->stage == BLOCK_REPLICATION_FAILOVER) {
         commit_job = &s->commit_job->job;
-        assert(commit_job->aio_context == qemu_get_current_aio_context());
         WITH_JOB_LOCK_GUARD() {
+            assert(commit_job->aio_context == qemu_get_current_aio_context());
             job_cancel_sync_locked(commit_job, false);
         }
     }
diff --git a/blockjob.c b/blockjob.c
index 04d868f020..afb0e9ad5e 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -154,12 +154,13 @@ static void child_job_set_aio_ctx(BdrvChild *c, AioContext *ctx,
         bdrv_set_aio_context_ignore(sibling->bs, ctx, ignore);
     }
 
-    job->job.aio_context = ctx;
+    job_set_aio_context(&job->job, ctx);
 }
 
 static AioContext *child_job_get_parent_aio_context(BdrvChild *c)
 {
     BlockJob *job = c->opaque;
+    assert(qemu_in_main_thread());
 
     return job->job.aio_context;
 }
diff --git a/include/qemu/job.h b/include/qemu/job.h
index dfbf2ea501..ca46e46f5b 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -75,7 +75,12 @@ typedef struct Job {
     ProgressMeter progress;
 
 
-    /** AioContext to run the job coroutine in */
+    /**
+     * AioContext to run the job coroutine in.
+     * This field can be read when holding either the BQL (so we are in
+     * the main loop) or the job_mutex.
+     * Instead, it can be only written when we hold *both* BQL and job_mutex.
+     */
     AioContext *aio_context;
 
     /** Reference count of the block job */
@@ -706,4 +711,16 @@ void job_dismiss_locked(Job **job, Error **errp);
 int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
                            Error **errp);
 
+/**
+ * Sets the @job->aio_context.
+ * Called with job_mutex *not* held.
+ *
+ * This function must run in the main thread to protect against
+ * concurrent read in job_finish_sync_locked(),
+ * takes the job_mutex lock to protect against the read in
+ * job_do_yield_locked(), and must be called when the coroutine
+ * is quiescent.
+ */
+void job_set_aio_context(Job *job, AioContext *ctx);
+
 #endif
diff --git a/job.c b/job.c
index f05850a337..7a07d25ec3 100644
--- a/job.c
+++ b/job.c
@@ -354,6 +354,17 @@ Job *job_get_locked(const char *id)
     return NULL;
 }
 
+void job_set_aio_context(Job *job, AioContext *ctx)
+{
+    /* protect against read in job_finish_sync_locked and job_start */
+    assert(qemu_in_main_thread());
+    /* protect against read in job_do_yield_locked */
+    JOB_LOCK_GUARD();
+    /* ensure the coroutine is quiescent while the AioContext is changed */
+    assert(job->pause_count > 0);
+    job->aio_context = ctx;
+}
+
 /* Called with job_mutex *not* held. */
 static void job_sleep_timer_cb(void *opaque)
 {
@@ -1256,6 +1267,7 @@ int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
 {
     Error *local_err = NULL;
     int ret;
+    assert(qemu_in_main_thread());
 
     job_ref_locked(job);
 
-- 
2.31.1

Re: [PATCH v5 18/20] jobs: protect job.aio_context with BQL and job_mutex

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 3336 bytes --]

On Tue, Feb 08, 2022 at 09:35:11AM -0500, Emanuele Giuseppe Esposito wrote:
>  static AioContext *child_job_get_parent_aio_context(BdrvChild *c)
>  {
>      BlockJob *job = c->opaque;
> +    assert(qemu_in_main_thread());
>  
>      return job->job.aio_context;
>  }

It's not clear to me that .get_parent_aio_context() should only be
called from the main thread. The API is read-only so someone might try
to call from I/O code in the future expecting it to work like other
read-only graph APIs that are available from I/O code.

Currently the assertion is true because the only user is
bdrv_attach_child_*() but please document this invariant for
bdrv_child_get_parent_aio_context() and the callback. Maybe move the
assertion into a higher-level function like
bdrv_child_get_parent_aio_context() (if that still covers all cases).

> diff --git a/include/qemu/job.h b/include/qemu/job.h
> index dfbf2ea501..ca46e46f5b 100644
> --- a/include/qemu/job.h
> +++ b/include/qemu/job.h
> @@ -75,7 +75,12 @@ typedef struct Job {
>      ProgressMeter progress;
>  
>  
> -    /** AioContext to run the job coroutine in */
> +    /**
> +     * AioContext to run the job coroutine in.
> +     * This field can be read when holding either the BQL (so we are in
> +     * the main loop) or the job_mutex.
> +     * Instead, it can be only written when we hold *both* BQL and job_mutex.

s/Instead,//

(It sounds weird because "instead" means "replacement" or "substitution"
We're comparing "read" and "write" here, not substituting them.
Something like "on the other hand" or "conversely" works.)

> +     */
>      AioContext *aio_context;
>  
>      /** Reference count of the block job */
> @@ -706,4 +711,16 @@ void job_dismiss_locked(Job **job, Error **errp);
>  int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
>                             Error **errp);
>  
> +/**
> + * Sets the @job->aio_context.
> + * Called with job_mutex *not* held.
> + *
> + * This function must run in the main thread to protect against
> + * concurrent read in job_finish_sync_locked(),
> + * takes the job_mutex lock to protect against the read in
> + * job_do_yield_locked(), and must be called when the coroutine
> + * is quiescent.
> + */
> +void job_set_aio_context(Job *job, AioContext *ctx);
> +
>  #endif
> diff --git a/job.c b/job.c
> index f05850a337..7a07d25ec3 100644
> --- a/job.c
> +++ b/job.c
> @@ -354,6 +354,17 @@ Job *job_get_locked(const char *id)
>      return NULL;
>  }
>  
> +void job_set_aio_context(Job *job, AioContext *ctx)
> +{
> +    /* protect against read in job_finish_sync_locked and job_start */
> +    assert(qemu_in_main_thread());
> +    /* protect against read in job_do_yield_locked */
> +    JOB_LOCK_GUARD();
> +    /* ensure the coroutine is quiescent while the AioContext is changed */
> +    assert(job->pause_count > 0);
> +    job->aio_context = ctx;
> +}
> +
>  /* Called with job_mutex *not* held. */
>  static void job_sleep_timer_cb(void *opaque)
>  {
> @@ -1256,6 +1267,7 @@ int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
>  {
>      Error *local_err = NULL;
>      int ret;
> +    assert(qemu_in_main_thread());
>  
>      job_ref_locked(job);
>  
> -- 
> 2.31.1
> 

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH v5 18/20] jobs: protect job.aio_context with BQL and job_mutex

[Emanuele Giuseppe Esposito]

Am 08/03/2022 um 14:41 schrieb Stefan Hajnoczi:
> It's not clear to me that .get_parent_aio_context() should only be
> called from the main thread. The API is read-only so someone might try
> to call from I/O code in the future expecting it to work like other
> read-only graph APIs that are available from I/O code.
> 
> Currently the assertion is true because the only user is
> bdrv_attach_child_*() but please document this invariant for
> bdrv_child_get_parent_aio_context() and the callback. Maybe move the
> assertion into a higher-level function like
> bdrv_child_get_parent_aio_context() (if that still covers all cases).

We classified .get_parent_aio_context as GS callback, and indeed
bdrv_child_get_parent_aio_context has the macro GLOBAL_STATE_CODE();
So we should be fine.

Emanuele

[PATCH v5 19/20] job.c: enable job lock/unlock and remove Aiocontext locks

[Emanuele Giuseppe Esposito]

Change the job_{lock/unlock} and macros to use job_mutex.

Now that they are not nop anymore, remove the aiocontext
to avoid deadlocks.

Therefore:
- when possible, remove completely the aiocontext lock/unlock pair
- if it is used by some other functions too, reduce the locking
section as much as possible, leaving the job API outside.

There is only one JobDriver callback, ->free() that assumes that
the aiocontext lock is held (because it calls bdrv_unref), so for
now keep that under aiocontext lock.

Also remove real_job_{lock/unlock}, as they are replaced by the
public functions.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 blockdev.c                       | 65 ++++-----------------------
 include/qemu/job.h               | 19 ++++----
 job-qmp.c                        | 41 ++++-------------
 job.c                            | 77 +++-----------------------------
 tests/unit/test-bdrv-drain.c     |  4 +-
 tests/unit/test-block-iothread.c |  2 +-
 tests/unit/test-blockjob.c       | 13 ++----
 7 files changed, 38 insertions(+), 183 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index fd436024b4..7d00850efe 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -155,12 +155,7 @@ void blockdev_mark_auto_del(BlockBackend *blk)
     for (job = block_job_next_locked(NULL); job;
          job = block_job_next_locked(job)) {
         if (block_job_has_bdrv(job, blk_bs(blk))) {
-            AioContext *aio_context = job->job.aio_context;
-            aio_context_acquire(aio_context);
-
             job_cancel_locked(&job->job, false);
-
-            aio_context_release(aio_context);
         }
     }
 
@@ -1836,16 +1831,9 @@ static void drive_backup_abort(BlkActionState *common)
     DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
 
     if (state->job) {
-        AioContext *aio_context;
-
-        aio_context = bdrv_get_aio_context(state->bs);
-        aio_context_acquire(aio_context);
-
         WITH_JOB_LOCK_GUARD() {
             job_cancel_sync_locked(&state->job->job, true);
         }
-
-        aio_context_release(aio_context);
     }
 }
 
@@ -1939,16 +1927,9 @@ static void blockdev_backup_abort(BlkActionState *common)
     BlockdevBackupState *state = DO_UPCAST(BlockdevBackupState, common, common);
 
     if (state->job) {
-        AioContext *aio_context;
-
-        aio_context = bdrv_get_aio_context(state->bs);
-        aio_context_acquire(aio_context);
-
         WITH_JOB_LOCK_GUARD() {
             job_cancel_sync_locked(&state->job->job, true);
         }
-
-        aio_context_release(aio_context);
     }
 }
 
@@ -3312,18 +3293,13 @@ out:
     aio_context_release(aio_context);
 }
 
-/*
- * Get a block job using its ID and acquire its AioContext.
- * Returns with job_lock held on success.
- */
-static BlockJob *find_block_job(const char *id, AioContext **aio_context,
-                                Error **errp)
+/* Get a block job using its ID. Returns with job_lock held on success */
+static BlockJob *find_block_job(const char *id, Error **errp)
 {
     BlockJob *job;
 
     assert(id != NULL);
 
-    *aio_context = NULL;
     job_lock();
 
     job = block_job_get_locked(id);
@@ -3335,31 +3311,25 @@ static BlockJob *find_block_job(const char *id, AioContext **aio_context,
         return NULL;
     }
 
-    *aio_context = block_job_get_aio_context(job);
-    aio_context_acquire(*aio_context);
-
     return job;
 }
 
 void qmp_block_job_set_speed(const char *device, int64_t speed, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job = find_block_job(device, errp);
 
     if (!job) {
         return;
     }
 
     block_job_set_speed_locked(job, speed, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_block_job_cancel(const char *device,
                           bool has_force, bool force, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job = find_block_job(device, errp);
 
     if (!job) {
         return;
@@ -3378,14 +3348,12 @@ void qmp_block_job_cancel(const char *device,
     trace_qmp_block_job_cancel(job);
     job_user_cancel_locked(&job->job, force, errp);
 out:
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_block_job_pause(const char *device, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job = find_block_job(device, errp);
 
     if (!job) {
         return;
@@ -3393,14 +3361,12 @@ void qmp_block_job_pause(const char *device, Error **errp)
 
     trace_qmp_block_job_pause(job);
     job_user_pause_locked(&job->job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_block_job_resume(const char *device, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job = find_block_job(device, errp);
 
     if (!job) {
         return;
@@ -3408,14 +3374,12 @@ void qmp_block_job_resume(const char *device, Error **errp)
 
     trace_qmp_block_job_resume(job);
     job_user_resume_locked(&job->job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_block_job_complete(const char *device, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job = find_block_job(device, errp);
 
     if (!job) {
         return;
@@ -3423,14 +3387,12 @@ void qmp_block_job_complete(const char *device, Error **errp)
 
     trace_qmp_block_job_complete(job);
     job_complete_locked(&job->job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_block_job_finalize(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *job = find_block_job(id, &aio_context, errp);
+    BlockJob *job = find_block_job(id, errp);
 
     if (!job) {
         return;
@@ -3440,21 +3402,13 @@ void qmp_block_job_finalize(const char *id, Error **errp)
     job_ref_locked(&job->job);
     job_finalize_locked(&job->job, errp);
 
-    /*
-     * Job's context might have changed via job_finalize_locked
-     * (and job_txn_apply automatically acquires the new one),
-     * so make sure we release the correct one.
-     */
-    aio_context = block_job_get_aio_context(job);
     job_unref_locked(&job->job);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_block_job_dismiss(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    BlockJob *bjob = find_block_job(id, &aio_context, errp);
+    BlockJob *bjob = find_block_job(id, errp);
     Job *job;
 
     if (!bjob) {
@@ -3464,7 +3418,6 @@ void qmp_block_job_dismiss(const char *id, Error **errp)
     trace_qmp_block_job_dismiss(bjob);
     job = &bjob->job;
     job_dismiss_locked(&job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
diff --git a/include/qemu/job.h b/include/qemu/job.h
index ca46e46f5b..574110a1f2 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -75,11 +75,14 @@ typedef struct Job {
     ProgressMeter progress;
 
 
+    /** Protected by job_mutex */
+
     /**
      * AioContext to run the job coroutine in.
-     * This field can be read when holding either the BQL (so we are in
-     * the main loop) or the job_mutex.
-     * Instead, it can be only written when we hold *both* BQL and job_mutex.
+     * The job Aiocontext can be read when holding *either*
+     * the BQL (so we are in the main loop) or the job_mutex.
+     * Instead, it can only be written when we hold *both* BQL
+     * and the job_mutex.
      */
     AioContext *aio_context;
 
@@ -104,7 +107,7 @@ typedef struct Job {
     /**
      * Set to false by the job while the coroutine has yielded and may be
      * re-entered by job_enter(). There may still be I/O or event loop activity
-     * pending. Accessed under block_job_mutex (in blockjob.c).
+     * pending. Accessed under job_mutex.
      *
      * When the job is deferred to the main loop, busy is true as long as the
      * bottom half is still pending.
@@ -320,9 +323,9 @@ typedef enum JobCreateFlags {
 
 extern QemuMutex job_mutex;
 
-#define JOB_LOCK_GUARD() /* QEMU_LOCK_GUARD(&job_mutex) */
+#define JOB_LOCK_GUARD() QEMU_LOCK_GUARD(&job_mutex)
 
-#define WITH_JOB_LOCK_GUARD() /* WITH_QEMU_LOCK_GUARD(&job_mutex) */
+#define WITH_JOB_LOCK_GUARD() WITH_QEMU_LOCK_GUARD(&job_mutex)
 
 /**
  * job_lock:
@@ -647,7 +650,6 @@ void job_user_cancel_locked(Job *job, bool force, Error **errp);
  * Returns the return value from the job if the job actually completed
  * during the call, or -ECANCELED if it was canceled.
  *
- * Callers must hold the AioContext lock of job->aio_context.
  * Called between job_lock and job_unlock.
  */
 int job_cancel_sync_locked(Job *job, bool force);
@@ -672,8 +674,6 @@ void job_cancel_sync_all(void);
  * function).
  *
  * Returns the return value from the job.
- *
- * Callers must hold the AioContext lock of job->aio_context.
  * Called between job_lock and job_unlock.
  */
 int job_complete_sync_locked(Job *job, Error **errp);
@@ -705,7 +705,6 @@ void job_dismiss_locked(Job **job, Error **errp);
  * Returns 0 if the job is successfully completed, -ECANCELED if the job was
  * cancelled before completing, and -errno in other error cases.
  *
- * Callers must hold the AioContext lock of job->aio_context.
  * Called between job_lock and job_unlock.
  */
 int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
diff --git a/job-qmp.c b/job-qmp.c
index 615e056fc4..858b3a28f5 100644
--- a/job-qmp.c
+++ b/job-qmp.c
@@ -29,15 +29,11 @@
 #include "qapi/error.h"
 #include "trace/trace-root.h"
 
-/*
- * Get a block job using its ID and acquire its AioContext.
- * Returns with job_lock held on success.
- */
-static Job *find_job(const char *id, AioContext **aio_context, Error **errp)
+/* Get a job using its ID. Returns with job_lock held on success. */
+static Job *find_job(const char *id, Error **errp)
 {
     Job *job;
 
-    *aio_context = NULL;
     job_lock();
 
     job = job_get_locked(id);
@@ -47,16 +43,12 @@ static Job *find_job(const char *id, AioContext **aio_context, Error **errp)
         return NULL;
     }
 
-    *aio_context = job->aio_context;
-    aio_context_acquire(*aio_context);
-
     return job;
 }
 
 void qmp_job_cancel(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job = find_job(id, errp);
 
     if (!job) {
         return;
@@ -64,14 +56,12 @@ void qmp_job_cancel(const char *id, Error **errp)
 
     trace_qmp_job_cancel(job);
     job_user_cancel_locked(job, true, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_job_pause(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job = find_job(id, errp);
 
     if (!job) {
         return;
@@ -79,14 +69,12 @@ void qmp_job_pause(const char *id, Error **errp)
 
     trace_qmp_job_pause(job);
     job_user_pause_locked(job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_job_resume(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job = find_job(id, errp);
 
     if (!job) {
         return;
@@ -94,14 +82,12 @@ void qmp_job_resume(const char *id, Error **errp)
 
     trace_qmp_job_resume(job);
     job_user_resume_locked(job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_job_complete(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job = find_job(id, errp);
 
     if (!job) {
         return;
@@ -109,14 +95,12 @@ void qmp_job_complete(const char *id, Error **errp)
 
     trace_qmp_job_complete(job);
     job_complete_locked(job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_job_finalize(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job = find_job(id, errp);
 
     if (!job) {
         return;
@@ -126,21 +110,13 @@ void qmp_job_finalize(const char *id, Error **errp)
     job_ref_locked(job);
     job_finalize_locked(job, errp);
 
-    /*
-     * Job's context might have changed via job_finalize_locked
-     * (and job_txn_apply automatically acquires the new one),
-     * so make sure we release the correct one.
-     */
-    aio_context = job->aio_context;
     job_unref_locked(job);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
 void qmp_job_dismiss(const char *id, Error **errp)
 {
-    AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job = find_job(id, errp);
 
     if (!job) {
         return;
@@ -148,7 +124,6 @@ void qmp_job_dismiss(const char *id, Error **errp)
 
     trace_qmp_job_dismiss(job);
     job_dismiss_locked(&job, errp);
-    aio_context_release(aio_context);
     job_unlock();
 }
 
diff --git a/job.c b/job.c
index 7a07d25ec3..c7a41d88d6 100644
--- a/job.c
+++ b/job.c
@@ -96,21 +96,11 @@ struct JobTxn {
 };
 
 void job_lock(void)
-{
-    /* nop */
-}
-
-void job_unlock(void)
-{
-    /* nop */
-}
-
-static void real_job_lock(void)
 {
     qemu_mutex_lock(&job_mutex);
 }
 
-static void real_job_unlock(void)
+void job_unlock(void)
 {
     qemu_mutex_unlock(&job_mutex);
 }
@@ -178,7 +168,6 @@ static int job_txn_apply_locked(Job *job, int fn(Job *))
      * twice - which would break AIO_WAIT_WHILE from within fn.
      */
     job_ref_locked(job);
-    aio_context_release(job->aio_context);
 
     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
         rc = fn(other_job);
@@ -187,11 +176,6 @@ static int job_txn_apply_locked(Job *job, int fn(Job *))
         }
     }
 
-    /*
-     * Note that job->aio_context might have been changed by calling fn, so we
-     * can't use a local variable to cache it.
-     */
-    aio_context_acquire(job->aio_context);
     job_unref_locked(job);
     return rc;
 }
@@ -456,7 +440,10 @@ void job_unref_locked(Job *job)
 
         if (job->driver->free) {
             job_unlock();
+            /* FIXME: aiocontext lock is required because cb calls blk_unref */
+            aio_context_acquire(job->aio_context);
             job->driver->free(job);
+            aio_context_release(job->aio_context);
             job_lock();
         }
 
@@ -529,20 +516,16 @@ void job_enter_cond_locked(Job *job, bool(*fn)(Job *job))
         return;
     }
 
-    real_job_lock();
     if (job->busy) {
-        real_job_unlock();
         return;
     }
 
     if (fn && !fn(job)) {
-        real_job_unlock();
         return;
     }
 
     timer_del(&job->sleep_timer);
     job->busy = true;
-    real_job_unlock();
     job_unlock();
     aio_co_wake(job->co);
     job_lock();
@@ -568,13 +551,11 @@ static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns)
 {
     AioContext *next_aio_context;
 
-    real_job_lock();
     if (ns != -1) {
         timer_mod(&job->sleep_timer, ns);
     }
     job->busy = false;
     job_event_idle_locked(job);
-    real_job_unlock();
     job_unlock();
     qemu_coroutine_yield();
     job_lock();
@@ -913,7 +894,6 @@ static void job_cancel_async_locked(Job *job, bool force)
 /* Called with job_mutex held. */
 static void job_completed_txn_abort_locked(Job *job)
 {
-    AioContext *ctx;
     JobTxn *txn = job->txn;
     Job *other_job;
 
@@ -926,54 +906,28 @@ static void job_completed_txn_abort_locked(Job *job)
     txn->aborting = true;
     job_txn_ref_locked(txn);
 
-    /*
-     * We can only hold the single job's AioContext lock while calling
-     * job_finalize_single_locked() because the finalization callbacks can
-     * involve calls of AIO_WAIT_WHILE(), which could deadlock otherwise.
-     * Note that the job's AioContext may change when it is finalized.
-     */
-    job_ref_locked(job);
-    aio_context_release(job->aio_context);
-
     /* Other jobs are effectively cancelled by us, set the status for
      * them; this job, however, may or may not be cancelled, depending
      * on the caller, so leave it. */
     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
         if (other_job != job) {
-            ctx = other_job->aio_context;
-            aio_context_acquire(ctx);
             /*
              * This is a transaction: If one job failed, no result will matter.
              * Therefore, pass force=true to terminate all other jobs as quickly
              * as possible.
              */
             job_cancel_async_locked(other_job, true);
-            aio_context_release(ctx);
         }
     }
     while (!QLIST_EMPTY(&txn->jobs)) {
         other_job = QLIST_FIRST(&txn->jobs);
-        /*
-         * The job's AioContext may change, so store it in @ctx so we
-         * release the same context that we have acquired before.
-         */
-        ctx = other_job->aio_context;
-        aio_context_acquire(ctx);
         if (!job_is_completed_locked(other_job)) {
             assert(job_cancel_requested_locked(other_job));
             job_finish_sync_locked(other_job, NULL, NULL);
         }
-        aio_context_release(ctx);
         job_finalize_single_locked(other_job);
     }
 
-    /*
-     * Use job_ref_locked()/job_unref_locked() so we can read the AioContext
-     * here even if the job went away during job_finalize_single_locked().
-     */
-    aio_context_acquire(job->aio_context);
-    job_unref_locked(job);
-
     job_txn_unref_locked(txn);
 }
 
@@ -1092,12 +1046,8 @@ static void job_completed_locked(Job *job)
 static void job_exit(void *opaque)
 {
     Job *job = (Job *)opaque;
-    AioContext *ctx;
     JOB_LOCK_GUARD();
 
-    job_ref_locked(job);
-    aio_context_acquire(job->aio_context);
-
     /* This is a lie, we're not quiescent, but still doing the completion
      * callbacks. However, completion callbacks tend to involve operations that
      * drain block nodes, and if .drained_poll still returned true, we would
@@ -1106,17 +1056,6 @@ static void job_exit(void *opaque)
     job_event_idle_locked(job);
 
     job_completed_locked(job);
-
-    /*
-     * Note that calling job_completed_locked can move the job to a different
-     * aio_context, so we cannot cache from above.
-     * job_txn_apply_locked takes care of
-     * acquiring the new lock, and we ref/unref to avoid job_completed_locked
-     * freeing the job underneath us.
-     */
-    ctx = job->aio_context;
-    job_unref_locked(job);
-    aio_context_release(ctx);
 }
 
 /**
@@ -1227,14 +1166,10 @@ int job_cancel_sync_locked(Job *job, bool force)
 void job_cancel_sync_all(void)
 {
     Job *job;
-    AioContext *aio_context;
 
     JOB_LOCK_GUARD();
     while ((job = job_next_locked(NULL))) {
-        aio_context = job->aio_context;
-        aio_context_acquire(aio_context);
         job_cancel_sync_locked(job, true);
-        aio_context_release(aio_context);
     }
 }
 
@@ -1281,8 +1216,8 @@ int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp),
     }
 
     job_unlock();
-    AIO_WAIT_WHILE(job->aio_context,
-                   (job_enter(job), !job_is_completed(job)));
+    AIO_WAIT_WHILE_UNLOCKED(job->aio_context,
+                            (job_enter(job), !job_is_completed(job)));
     job_lock();
 
     ret = (job_is_cancelled_locked(job) && job->ret == 0)
diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index 0db056ea63..4924ceb562 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -930,9 +930,9 @@ static void test_blockjob_common_drain_node(enum drain_type drain_type,
         tjob->prepare_ret = -EIO;
         break;
     }
+    aio_context_release(ctx);
 
     job_start(&job->job);
-    aio_context_release(ctx);
 
     if (use_iothread) {
         /* job_co_entry() is run in the I/O thread, wait for the actual job
@@ -1016,12 +1016,12 @@ static void test_blockjob_common_drain_node(enum drain_type drain_type,
         g_assert_true(job->job.busy); /* We're in qemu_co_sleep_ns() */
     }
 
-    aio_context_acquire(ctx);
     WITH_JOB_LOCK_GUARD() {
         ret = job_complete_sync_locked(&job->job, &error_abort);
     }
     g_assert_cmpint(ret, ==, (result == TEST_JOB_SUCCESS ? 0 : -EIO));
 
+    aio_context_acquire(ctx);
     if (use_iothread) {
         blk_set_aio_context(blk_src, qemu_get_aio_context(), &error_abort);
         assert(blk_get_aio_context(blk_target) == qemu_get_aio_context());
diff --git a/tests/unit/test-block-iothread.c b/tests/unit/test-block-iothread.c
index 89e7f0fffb..9d7c8be00f 100644
--- a/tests/unit/test-block-iothread.c
+++ b/tests/unit/test-block-iothread.c
@@ -455,10 +455,10 @@ static void test_attach_blockjob(void)
         aio_poll(qemu_get_aio_context(), false);
     }
 
-    aio_context_acquire(ctx);
     WITH_JOB_LOCK_GUARD() {
         job_complete_sync_locked(&tjob->common.job, &error_abort);
     }
+    aio_context_acquire(ctx);
     blk_set_aio_context(blk, qemu_get_aio_context(), &error_abort);
     aio_context_release(ctx);
 
diff --git a/tests/unit/test-blockjob.c b/tests/unit/test-blockjob.c
index 8280b1e0c9..d6fc52f80a 100644
--- a/tests/unit/test-blockjob.c
+++ b/tests/unit/test-blockjob.c
@@ -228,10 +228,6 @@ static void cancel_common(CancelJob *s)
     BlockJob *job = &s->common;
     BlockBackend *blk = s->blk;
     JobStatus sts = job->job.status;
-    AioContext *ctx;
-
-    ctx = job->job.aio_context;
-    aio_context_acquire(ctx);
 
     WITH_JOB_LOCK_GUARD() {
         job_cancel_sync_locked(&job->job, true);
@@ -244,7 +240,6 @@ static void cancel_common(CancelJob *s)
     }
     destroy_blk(blk);
 
-    aio_context_release(ctx);
 }
 
 static void test_cancel_created(void)
@@ -405,11 +400,9 @@ static void test_cancel_concluded(void)
     aio_poll(qemu_get_aio_context(), true);
     assert(job->status == JOB_STATUS_PENDING);
 
-    aio_context_acquire(job->aio_context);
     WITH_JOB_LOCK_GUARD() {
         job_finalize_locked(job, &error_abort);
     }
-    aio_context_release(job->aio_context);
     assert(job->status == JOB_STATUS_CONCLUDED);
 
     cancel_common(s);
@@ -503,13 +496,11 @@ static void test_complete_in_standby(void)
 
     /* Wait for the job to become READY */
     job_start(job);
-    aio_context_acquire(ctx);
     /*
      * Here we are waiting for the status to change, so don't bother
      * protecting the read every time.
      */
-    AIO_WAIT_WHILE(ctx, job->status != JOB_STATUS_READY);
-    aio_context_release(ctx);
+    AIO_WAIT_WHILE_UNLOCKED(ctx, job->status != JOB_STATUS_READY);
 
     /* Begin the drained section, pausing the job */
     bdrv_drain_all_begin();
@@ -529,6 +520,7 @@ static void test_complete_in_standby(void)
         job_complete_locked(job, &error_abort);
 
         /* The test is done now, clean up. */
+        aio_context_release(ctx);
         job_finish_sync_locked(job, NULL, &error_abort);
         assert(job->status == JOB_STATUS_PENDING);
 
@@ -538,6 +530,7 @@ static void test_complete_in_standby(void)
         job_dismiss_locked(&job, &error_abort);
     }
 
+    aio_context_acquire(ctx);
     destroy_blk(blk);
     aio_context_release(ctx);
     iothread_join(iothread);
-- 
2.31.1

Re: [PATCH v5 19/20] job.c: enable job lock/unlock and remove Aiocontext locks

[Stefan Hajnoczi]

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On Tue, Feb 08, 2022 at 09:35:12AM -0500, Emanuele Giuseppe Esposito wrote:
> diff --git a/include/qemu/job.h b/include/qemu/job.h
> index ca46e46f5b..574110a1f2 100644
> --- a/include/qemu/job.h
> +++ b/include/qemu/job.h
> @@ -75,11 +75,14 @@ typedef struct Job {
>      ProgressMeter progress;
>  
>  
> +    /** Protected by job_mutex */
> +
>      /**
>       * AioContext to run the job coroutine in.
> -     * This field can be read when holding either the BQL (so we are in
> -     * the main loop) or the job_mutex.
> -     * Instead, it can be only written when we hold *both* BQL and job_mutex.
> +     * The job Aiocontext can be read when holding *either*
> +     * the BQL (so we are in the main loop) or the job_mutex.
> +     * Instead, it can only be written when we hold *both* BQL

s/Instead,//

> @@ -456,7 +440,10 @@ void job_unref_locked(Job *job)
>  
>          if (job->driver->free) {
>              job_unlock();
> +            /* FIXME: aiocontext lock is required because cb calls blk_unref */
> +            aio_context_acquire(job->aio_context);

We break the locking rules for job->aio_context here because the job is
already being destroyed and there can be no races? Can we avoid the
special case:

  AioContext *aio_context = job->aio_context;

  job_unlock();
  /* FIXME: aiocontext lock is required because cb calls blk_unref */
  aio_context_acquire(aio_context);
  job->driver->free(job);
  aio_context_release(aio_context);
  job_lock();

?

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Re: [PATCH v5 19/20] job.c: enable job lock/unlock and remove Aiocontext locks

[Emanuele Giuseppe Esposito]

Am 08/03/2022 um 15:04 schrieb Stefan Hajnoczi:
> On Tue, Feb 08, 2022 at 09:35:12AM -0500, Emanuele Giuseppe Esposito wrote:
>> diff --git a/include/qemu/job.h b/include/qemu/job.h
>> index ca46e46f5b..574110a1f2 100644
>> --- a/include/qemu/job.h
>> +++ b/include/qemu/job.h
>> @@ -75,11 +75,14 @@ typedef struct Job {
>>      ProgressMeter progress;
>>  
>>  
>> +    /** Protected by job_mutex */
>> +
>>      /**
>>       * AioContext to run the job coroutine in.
>> -     * This field can be read when holding either the BQL (so we are in
>> -     * the main loop) or the job_mutex.
>> -     * Instead, it can be only written when we hold *both* BQL and job_mutex.
>> +     * The job Aiocontext can be read when holding *either*
>> +     * the BQL (so we are in the main loop) or the job_mutex.
>> +     * Instead, it can only be written when we hold *both* BQL
> 
> s/Instead,//
> 
>> @@ -456,7 +440,10 @@ void job_unref_locked(Job *job)
>>  
>>          if (job->driver->free) {
>>              job_unlock();
>> +            /* FIXME: aiocontext lock is required because cb calls blk_unref */
>> +            aio_context_acquire(job->aio_context);
> 
> We break the locking rules for job->aio_context here because the job is
> already being destroyed and there can be no races? Can we avoid the
> special case:
> 
>   AioContext *aio_context = job->aio_context;
> 
>   job_unlock();
>   /* FIXME: aiocontext lock is required because cb calls blk_unref */
>   aio_context_acquire(aio_context);
>   job->driver->free(job);
>   aio_context_release(aio_context);
>   job_lock();
> 
> ?
> 
Makes sense.

Emanuele

[PATCH v5 20/20] block_job_query: remove atomic read

[Emanuele Giuseppe Esposito]

Not sure what the atomic here was supposed to do, since job.busy
is protected by the job lock. Since the whole function
is called under job_mutex, just remove the atomic.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 blockjob.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/blockjob.c b/blockjob.c
index afb0e9ad5e..e7ed4f545d 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -329,7 +329,7 @@ BlockJobInfo *block_job_query_locked(BlockJob *job, Error **errp)
     info = g_new0(BlockJobInfo, 1);
     info->type      = g_strdup(job_type_str(&job->job));
     info->device    = g_strdup(job->job.id);
-    info->busy      = qatomic_read(&job->job.busy);
+    info->busy      = job->job.busy;
     info->paused    = job->job.pause_count > 0;
     info->offset    = progress_current;
     info->len       = progress_total;
-- 
2.31.1

Re: [PATCH v5 20/20] block_job_query: remove atomic read

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 461 bytes --]

On Tue, Feb 08, 2022 at 09:35:13AM -0500, Emanuele Giuseppe Esposito wrote:
> Not sure what the atomic here was supposed to do, since job.busy
> is protected by the job lock. Since the whole function
> is called under job_mutex, just remove the atomic.
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  blockjob.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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