[Qemu-devel] [PULL 0/7] monitor: Thread safety improvements

[Qemu-devel] [PULL 0/7] monitor: Thread safety improvements

[Markus Armbruster]

The following changes since commit 2ef2f16781af9dee6ba6517755e9073ba5799fa2:

  Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20180615a' into staging (2018-06-15 18:13:35 +0100)

are available in the Git repository at:

  git://repo.or.cz/qemu/armbru.git tags/pull-monitor-2018-06-18

for you to fetch changes up to 474514668b47c9d2148b526e379ffbb6764d9a9e:

  monitor: add lock to protect mon_fdsets (2018-06-18 15:48:22 +0200)

----------------------------------------------------------------
Monitor patches for 2018-06-18

----------------------------------------------------------------
Peter Xu (7):
      monitor: rename out_lock to mon_lock
      monitor: protect mon->fds with mon_lock
      monitor: more comments on lock-free elements
      monitor: fix comment for monitor_lock
      monitor: remove event_clock_type
      monitor: move init global earlier
      monitor: add lock to protect mon_fdsets

 monitor.c     | 168 ++++++++++++++++++++++++++++++++++++++++------------------
 stubs/fdset.c |   2 +-
 util/osdep.c  |   3 +-
 vl.c          |   7 +--
 4 files changed, 121 insertions(+), 59 deletions(-)

Peter Xu (7):
  monitor: rename out_lock to mon_lock
  monitor: protect mon->fds with mon_lock
  monitor: more comments on lock-free elements
  monitor: fix comment for monitor_lock
  monitor: remove event_clock_type
  monitor: move init global earlier
  monitor: add lock to protect mon_fdsets

 monitor.c     | 168 +++++++++++++++++++++++++++++++++++---------------
 stubs/fdset.c |   2 +-
 util/osdep.c  |   3 +-
 vl.c          |   7 +--
 4 files changed, 121 insertions(+), 59 deletions(-)

-- 
2.17.1

[Qemu-devel] [PULL 1/7] monitor: rename out_lock to mon_lock

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

The out_lock is protecting a few Monitor fields.  In the future the
monitor code will start to run in multiple threads.  We are going to
turn it into a bigger lock to protect not only the out buffer but also
most of the rest.

Since at it, rearrange the Monitor struct a bit.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-2-peterx@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 monitor.c | 53 +++++++++++++++++++++++++++++------------------------
 1 file changed, 29 insertions(+), 24 deletions(-)

diff --git a/monitor.c b/monitor.c
index 6d0cec552e..5bc9b2dcd0 100644
--- a/monitor.c
+++ b/monitor.c
@@ -206,15 +206,6 @@ struct Monitor {
     int suspend_cnt;            /* Needs to be accessed atomically */
     bool skip_flush;
     bool use_io_thr;
-
-    /* We can't access guest memory when holding the lock */
-    QemuMutex out_lock;
-    QString *outbuf;
-    guint out_watch;
-
-    /* Read under either BQL or out_lock, written with BQL+out_lock.  */
-    int mux_out;
-
     ReadLineState *rs;
     MonitorQMP qmp;
     gchar *mon_cpu_path;
@@ -223,6 +214,20 @@ struct Monitor {
     mon_cmd_t *cmd_table;
     QLIST_HEAD(,mon_fd_t) fds;
     QTAILQ_ENTRY(Monitor) entry;
+
+    /*
+     * The per-monitor lock. We can't access guest memory when holding
+     * the lock.
+     */
+    QemuMutex mon_lock;
+
+    /*
+     * Fields that are protected by the per-monitor lock.
+     */
+    QString *outbuf;
+    guint out_watch;
+    /* Read under either BQL or mon_lock, written with BQL+mon_lock.  */
+    int mux_out;
 };
 
 /* Let's add monitor global variables to this struct. */
@@ -365,14 +370,14 @@ static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond,
 {
     Monitor *mon = opaque;
 
-    qemu_mutex_lock(&mon->out_lock);
+    qemu_mutex_lock(&mon->mon_lock);
     mon->out_watch = 0;
     monitor_flush_locked(mon);
-    qemu_mutex_unlock(&mon->out_lock);
+    qemu_mutex_unlock(&mon->mon_lock);
     return FALSE;
 }
 
-/* Called with mon->out_lock held.  */
+/* Called with mon->mon_lock held.  */
 static void monitor_flush_locked(Monitor *mon)
 {
     int rc;
@@ -410,9 +415,9 @@ static void monitor_flush_locked(Monitor *mon)
 
 void monitor_flush(Monitor *mon)
 {
-    qemu_mutex_lock(&mon->out_lock);
+    qemu_mutex_lock(&mon->mon_lock);
     monitor_flush_locked(mon);
-    qemu_mutex_unlock(&mon->out_lock);
+    qemu_mutex_unlock(&mon->mon_lock);
 }
 
 /* flush at every end of line */
@@ -420,7 +425,7 @@ static void monitor_puts(Monitor *mon, const char *str)
 {
     char c;
 
-    qemu_mutex_lock(&mon->out_lock);
+    qemu_mutex_lock(&mon->mon_lock);
     for(;;) {
         c = *str++;
         if (c == '\0')
@@ -433,7 +438,7 @@ static void monitor_puts(Monitor *mon, const char *str)
             monitor_flush_locked(mon);
         }
     }
-    qemu_mutex_unlock(&mon->out_lock);
+    qemu_mutex_unlock(&mon->mon_lock);
 }
 
 void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
@@ -724,7 +729,7 @@ static void monitor_data_init(Monitor *mon, bool skip_flush,
                               bool use_io_thr)
 {
     memset(mon, 0, sizeof(Monitor));
-    qemu_mutex_init(&mon->out_lock);
+    qemu_mutex_init(&mon->mon_lock);
     qemu_mutex_init(&mon->qmp.qmp_queue_lock);
     mon->outbuf = qstring_new();
     /* Use *mon_cmds by default. */
@@ -744,7 +749,7 @@ static void monitor_data_destroy(Monitor *mon)
     }
     readline_free(mon->rs);
     qobject_unref(mon->outbuf);
-    qemu_mutex_destroy(&mon->out_lock);
+    qemu_mutex_destroy(&mon->mon_lock);
     qemu_mutex_destroy(&mon->qmp.qmp_queue_lock);
     monitor_qmp_cleanup_req_queue_locked(mon);
     monitor_qmp_cleanup_resp_queue_locked(mon);
@@ -776,13 +781,13 @@ char *qmp_human_monitor_command(const char *command_line, bool has_cpu_index,
     handle_hmp_command(&hmp, command_line);
     cur_mon = old_mon;
 
-    qemu_mutex_lock(&hmp.out_lock);
+    qemu_mutex_lock(&hmp.mon_lock);
     if (qstring_get_length(hmp.outbuf) > 0) {
         output = g_strdup(qstring_get_str(hmp.outbuf));
     } else {
         output = g_strdup("");
     }
-    qemu_mutex_unlock(&hmp.out_lock);
+    qemu_mutex_unlock(&hmp.mon_lock);
 
 out:
     monitor_data_destroy(&hmp);
@@ -4381,9 +4386,9 @@ static void monitor_event(void *opaque, int event)
 
     switch (event) {
     case CHR_EVENT_MUX_IN:
-        qemu_mutex_lock(&mon->out_lock);
+        qemu_mutex_lock(&mon->mon_lock);
         mon->mux_out = 0;
-        qemu_mutex_unlock(&mon->out_lock);
+        qemu_mutex_unlock(&mon->mon_lock);
         if (mon->reset_seen) {
             readline_restart(mon->rs);
             monitor_resume(mon);
@@ -4403,9 +4408,9 @@ static void monitor_event(void *opaque, int event)
         } else {
             atomic_inc(&mon->suspend_cnt);
         }
-        qemu_mutex_lock(&mon->out_lock);
+        qemu_mutex_lock(&mon->mon_lock);
         mon->mux_out = 1;
-        qemu_mutex_unlock(&mon->out_lock);
+        qemu_mutex_unlock(&mon->mon_lock);
         break;
 
     case CHR_EVENT_OPENED:
-- 
2.17.1

[Qemu-devel] [PULL 2/7] monitor: protect mon->fds with mon_lock

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

mon->fds were protected by BQL.  Now protect it by mon_lock so that it
can even be used in monitor iothread.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-3-peterx@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 monitor.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/monitor.c b/monitor.c
index 5bc9b2dcd0..0fba3ccc20 100644
--- a/monitor.c
+++ b/monitor.c
@@ -212,7 +212,6 @@ struct Monitor {
     BlockCompletionFunc *password_completion_cb;
     void *password_opaque;
     mon_cmd_t *cmd_table;
-    QLIST_HEAD(,mon_fd_t) fds;
     QTAILQ_ENTRY(Monitor) entry;
 
     /*
@@ -224,6 +223,7 @@ struct Monitor {
     /*
      * Fields that are protected by the per-monitor lock.
      */
+    QLIST_HEAD(, mon_fd_t) fds;
     QString *outbuf;
     guint out_watch;
     /* Read under either BQL or mon_lock, written with BQL+mon_lock.  */
@@ -2187,7 +2187,7 @@ static void hmp_acl_remove(Monitor *mon, const QDict *qdict)
 void qmp_getfd(const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
-    int fd;
+    int fd, tmp_fd;
 
     fd = qemu_chr_fe_get_msgfd(&cur_mon->chr);
     if (fd == -1) {
@@ -2202,13 +2202,17 @@ void qmp_getfd(const char *fdname, Error **errp)
         return;
     }
 
+    qemu_mutex_lock(&cur_mon->mon_lock);
     QLIST_FOREACH(monfd, &cur_mon->fds, next) {
         if (strcmp(monfd->name, fdname) != 0) {
             continue;
         }
 
-        close(monfd->fd);
+        tmp_fd = monfd->fd;
         monfd->fd = fd;
+        qemu_mutex_unlock(&cur_mon->mon_lock);
+        /* Make sure close() is out of critical section */
+        close(tmp_fd);
         return;
     }
 
@@ -2217,24 +2221,31 @@ void qmp_getfd(const char *fdname, Error **errp)
     monfd->fd = fd;
 
     QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
+    qemu_mutex_unlock(&cur_mon->mon_lock);
 }
 
 void qmp_closefd(const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
+    int tmp_fd;
 
+    qemu_mutex_lock(&cur_mon->mon_lock);
     QLIST_FOREACH(monfd, &cur_mon->fds, next) {
         if (strcmp(monfd->name, fdname) != 0) {
             continue;
         }
 
         QLIST_REMOVE(monfd, next);
-        close(monfd->fd);
+        tmp_fd = monfd->fd;
         g_free(monfd->name);
         g_free(monfd);
+        qemu_mutex_unlock(&cur_mon->mon_lock);
+        /* Make sure close() is out of critical section */
+        close(tmp_fd);
         return;
     }
 
+    qemu_mutex_unlock(&cur_mon->mon_lock);
     error_setg(errp, QERR_FD_NOT_FOUND, fdname);
 }
 
@@ -2242,6 +2253,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
 
+    qemu_mutex_lock(&mon->mon_lock);
     QLIST_FOREACH(monfd, &mon->fds, next) {
         int fd;
 
@@ -2255,10 +2267,12 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
         QLIST_REMOVE(monfd, next);
         g_free(monfd->name);
         g_free(monfd);
+        qemu_mutex_unlock(&mon->mon_lock);
 
         return fd;
     }
 
+    qemu_mutex_unlock(&mon->mon_lock);
     error_setg(errp, "File descriptor named '%s' has not been found", fdname);
     return -1;
 }
-- 
2.17.1

[Qemu-devel] [PULL 3/7] monitor: more comments on lock-free elements

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

Add some explicit comments for both Readline and cpu_set/cpu_get helpers
that they do not need the mon_lock protection.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-4-peterx@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 monitor.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/monitor.c b/monitor.c
index 0fba3ccc20..5c60bf08cc 100644
--- a/monitor.c
+++ b/monitor.c
@@ -206,7 +206,15 @@ struct Monitor {
     int suspend_cnt;            /* Needs to be accessed atomically */
     bool skip_flush;
     bool use_io_thr;
+
+    /*
+     * State used only in the thread "owning" the monitor.
+     * If @use_io_thr, this is mon_global.mon_iothread.
+     * Else, it's the main thread.
+     * These members can be safely accessed without locks.
+     */
     ReadLineState *rs;
+
     MonitorQMP qmp;
     gchar *mon_cpu_path;
     BlockCompletionFunc *password_completion_cb;
@@ -1311,7 +1319,7 @@ void qmp_qmp_capabilities(bool has_enable, QMPCapabilityList *enable,
     cur_mon->qmp.commands = &qmp_commands;
 }
 
-/* set the current CPU defined by the user */
+/* Set the current CPU defined by the user. Callers must hold BQL. */
 int monitor_set_cpu(int cpu_index)
 {
     CPUState *cpu;
@@ -1325,6 +1333,7 @@ int monitor_set_cpu(int cpu_index)
     return 0;
 }
 
+/* Callers must hold BQL. */
 static CPUState *mon_get_cpu_sync(bool synchronize)
 {
     CPUState *cpu;
-- 
2.17.1

[Qemu-devel] [PULL 4/7] monitor: fix comment for monitor_lock

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

Fix typo in d622cb5879c.  Meanwhile move these variables close to each
other.  monitor_qapi_event_state can be declared static, add that.

Reported-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-5-peterx@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 monitor.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/monitor.c b/monitor.c
index 5c60bf08cc..fa9c35631f 100644
--- a/monitor.c
+++ b/monitor.c
@@ -266,10 +266,11 @@ typedef struct QMPRequest QMPRequest;
 /* QMP checker flags */
 #define QMP_ACCEPT_UNKNOWNS 1
 
-/* Protects mon_list, monitor_event_state.  */
+/* Protects mon_list, monitor_qapi_event_state.  */
 static QemuMutex monitor_lock;
-
+static GHashTable *monitor_qapi_event_state;
 static QTAILQ_HEAD(mon_list, Monitor) mon_list;
+
 static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets;
 static int mon_refcount;
 
@@ -571,8 +572,6 @@ static MonitorQAPIEventConf monitor_qapi_event_conf[QAPI_EVENT__MAX] = {
     [QAPI_EVENT_VSERPORT_CHANGE]   = { 1000 * SCALE_MS },
 };
 
-GHashTable *monitor_qapi_event_state;
-
 /*
  * Emits the event to every monitor instance, @event is only used for trace
  * Called with monitor_lock held.
-- 
2.17.1

[Qemu-devel] [PULL 5/7] monitor: remove event_clock_type

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

Instead, use a dynamic function to detect which clock we'll use.  The
problem is that the old code will let monitor initialization depend on
configure_accelerator() (that's where qtest_enabled() start to take
effect).  After this change, we don't have such a dependency any more.
We just need to make sure configure_accelerator() is called when we
start to use it.  Now it's only used in monitor_qapi_event_queue() and
monitor_qapi_event_handler(), so we're good.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-6-peterx@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[monitor_get_event_clock() name and comment tweaked]
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 monitor.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/monitor.c b/monitor.c
index fa9c35631f..e805e40799 100644
--- a/monitor.c
+++ b/monitor.c
@@ -281,8 +281,6 @@ QmpCommandList qmp_commands, qmp_cap_negotiation_commands;
 
 Monitor *cur_mon;
 
-static QEMUClockType event_clock_type = QEMU_CLOCK_REALTIME;
-
 static void monitor_command_cb(void *opaque, const char *cmdline,
                                void *readline_opaque);
 
@@ -309,6 +307,19 @@ static inline bool monitor_is_hmp_non_interactive(const Monitor *mon)
     return !monitor_is_qmp(mon) && !monitor_uses_readline(mon);
 }
 
+/*
+ * Return the clock to use for recording an event's time.
+ * Beware: result is invalid before configure_accelerator().
+ */
+static inline QEMUClockType monitor_get_event_clock(void)
+{
+    /*
+     * This allows us to perform tests on the monitor queues to verify
+     * that the rate limits are enforced.
+     */
+    return qtest_enabled() ? QEMU_CLOCK_VIRTUAL : QEMU_CLOCK_REALTIME;
+}
+
 /**
  * Is the current monitor, if any, a QMP monitor?
  */
@@ -632,7 +643,7 @@ monitor_qapi_event_queue(QAPIEvent event, QDict *qdict, Error **errp)
              * monitor_qapi_event_handler() in evconf->rate ns.  Any
              * events arriving before then will be delayed until then.
              */
-            int64_t now = qemu_clock_get_ns(event_clock_type);
+            int64_t now = qemu_clock_get_ns(monitor_get_event_clock());
 
             monitor_qapi_event_emit(event, qdict);
 
@@ -640,7 +651,7 @@ monitor_qapi_event_queue(QAPIEvent event, QDict *qdict, Error **errp)
             evstate->event = event;
             evstate->data = qobject_ref(data);
             evstate->qdict = NULL;
-            evstate->timer = timer_new_ns(event_clock_type,
+            evstate->timer = timer_new_ns(monitor_get_event_clock(),
                                           monitor_qapi_event_handler,
                                           evstate);
             g_hash_table_add(monitor_qapi_event_state, evstate);
@@ -665,7 +676,7 @@ static void monitor_qapi_event_handler(void *opaque)
     qemu_mutex_lock(&monitor_lock);
 
     if (evstate->qdict) {
-        int64_t now = qemu_clock_get_ns(event_clock_type);
+        int64_t now = qemu_clock_get_ns(monitor_get_event_clock());
 
         monitor_qapi_event_emit(evstate->event, evstate->qdict);
         qobject_unref(evstate->qdict);
@@ -721,10 +732,6 @@ static gboolean qapi_event_throttle_equal(const void *a, const void *b)
 
 static void monitor_qapi_event_init(void)
 {
-    if (qtest_enabled()) {
-        event_clock_type = QEMU_CLOCK_VIRTUAL;
-    }
-
     monitor_qapi_event_state = g_hash_table_new(qapi_event_throttle_hash,
                                                 qapi_event_throttle_equal);
     qmp_event_set_func_emit(monitor_qapi_event_queue);
-- 
2.17.1

[Qemu-devel] [PULL 6/7] monitor: move init global earlier

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

Before this patch, monitor fd helpers might be called even earlier than
monitor_init_globals().  This can be problematic.

After previous work, now monitor_init_globals() does not depend on
accelerator initialization any more.  Call it earlier (before CLI
parsing; that's where the monitor APIs might be called) to make sure it
is called before any of the monitor APIs.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-7-peterx@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 vl.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/vl.c b/vl.c
index 6e34fb348d..b3426e03d0 100644
--- a/vl.c
+++ b/vl.c
@@ -2978,6 +2978,7 @@ int main(int argc, char **argv, char **envp)
 
     runstate_init();
     postcopy_infrastructure_init();
+    monitor_init_globals();
 
     if (qcrypto_init(&err) < 0) {
         error_reportf_err(err, "cannot initialize crypto: ");
@@ -4412,12 +4413,6 @@ int main(int argc, char **argv, char **envp)
     default_drive(default_floppy, snapshot, IF_FLOPPY, 0, FD_OPTS);
     default_drive(default_sdcard, snapshot, IF_SD, 0, SD_OPTS);
 
-    /*
-     * Note: qtest_enabled() (which is used in monitor_qapi_event_init())
-     * depends on configure_accelerator() above.
-     */
-    monitor_init_globals();
-
     if (qemu_opts_foreach(qemu_find_opts("mon"),
                           mon_init_func, NULL, NULL)) {
         exit(1);
-- 
2.17.1

Re: [Qemu-devel] [PULL 6/7] monitor: move init global earlier

[Wolfgang Bumiller]

On Mon, Jun 18, 2018 at 04:08:53PM +0200, Markus Armbruster wrote:
> From: Peter Xu <peterx@redhat.com>
> 
> Before this patch, monitor fd helpers might be called even earlier than
> monitor_init_globals().  This can be problematic.
> 
> After previous work, now monitor_init_globals() does not depend on
> accelerator initialization any more.  Call it earlier (before CLI
> parsing; that's where the monitor APIs might be called) to make sure it
> is called before any of the monitor APIs.

It looks like this patch moves the creation of the 'IO mon_iothread' to
before the call to os_daemonize().
With qemu 3.0 I'm experiencing crashes when shutting down daemonized
qemu instances, at pthread_join() on the 'IO mon_iothread' thread.

monitor_init_globals() calls monitor_iothread_init(), which in turn uses
iothread_create() to create a joinable thread. Then os_daemonize() is
called after which the thread is no longer "ours".
Debug-writing the thread IDs at pthread_create() and pthread_join()
together with the 'detachable' flag revealed that the mon_iothread ID is
already being reused, in my trace for a detached thread, and the join
then ends with a coredump and ugly log output.

> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> Message-Id: <20180608035511.7439-7-peterx@redhat.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  vl.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/vl.c b/vl.c
> index 6e34fb348d..b3426e03d0 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2978,6 +2978,7 @@ int main(int argc, char **argv, char **envp)
>  
>      runstate_init();
>      postcopy_infrastructure_init();
> +    monitor_init_globals();
>  
>      if (qcrypto_init(&err) < 0) {
>          error_reportf_err(err, "cannot initialize crypto: ");
> @@ -4412,12 +4413,6 @@ int main(int argc, char **argv, char **envp)
>      default_drive(default_floppy, snapshot, IF_FLOPPY, 0, FD_OPTS);
>      default_drive(default_sdcard, snapshot, IF_SD, 0, SD_OPTS);
>  
> -    /*
> -     * Note: qtest_enabled() (which is used in monitor_qapi_event_init())
> -     * depends on configure_accelerator() above.
> -     */
> -    monitor_init_globals();
> -
>      if (qemu_opts_foreach(qemu_find_opts("mon"),
>                            mon_init_func, NULL, NULL)) {
>          exit(1);
> -- 
> 2.17.1

Re: [Qemu-devel] [PULL 6/7] monitor: move init global earlier

[Peter Xu]

On Wed, Sep 05, 2018 at 05:05:10PM +0200, Wolfgang Bumiller wrote:
> On Mon, Jun 18, 2018 at 04:08:53PM +0200, Markus Armbruster wrote:
> > From: Peter Xu <peterx@redhat.com>
> > 
> > Before this patch, monitor fd helpers might be called even earlier than
> > monitor_init_globals().  This can be problematic.
> > 
> > After previous work, now monitor_init_globals() does not depend on
> > accelerator initialization any more.  Call it earlier (before CLI
> > parsing; that's where the monitor APIs might be called) to make sure it
> > is called before any of the monitor APIs.
> 
> It looks like this patch moves the creation of the 'IO mon_iothread' to
> before the call to os_daemonize().
> With qemu 3.0 I'm experiencing crashes when shutting down daemonized
> qemu instances, at pthread_join() on the 'IO mon_iothread' thread.
> 
> monitor_init_globals() calls monitor_iothread_init(), which in turn uses
> iothread_create() to create a joinable thread. Then os_daemonize() is
> called after which the thread is no longer "ours".
> Debug-writing the thread IDs at pthread_create() and pthread_join()
> together with the 'detachable' flag revealed that the mon_iothread ID is
> already being reused, in my trace for a detached thread, and the join
> then ends with a coredump and ugly log output.

Indeed.  So we have these ordering constraints:

  init mon locks [1]
  cli parsing
  daemonize
  create mon iothread [2]

I can't figure out a way unless we split the global init routine for
the monitors, possibly (and simply) by postpone creation of the
iothread.  Thoughts?

(Note that AFAICT Markus is on holiday and will be back after two weeks)

Regards,

-- 
Peter Xu

[Qemu-devel] [PULL 7/7] monitor: add lock to protect mon_fdsets

[Markus Armbruster]

From: Peter Xu <peterx@redhat.com>

Introduce a new global big lock for mon_fdsets.  Take it where needed.

The monitor_fdset_get_fd() handling is a bit tricky: now we need to call
qemu_mutex_unlock() which might pollute errno, so we need to make sure
the correct errno be passed up to the callers.  To make things simpler,
we let monitor_fdset_get_fd() return the -errno directly when error
happens, then in qemu_open() we move it back into errno.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180608035511.7439-8-peterx@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 monitor.c     | 52 +++++++++++++++++++++++++++++++++++++++++----------
 stubs/fdset.c |  2 +-
 util/osdep.c  |  3 ++-
 3 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/monitor.c b/monitor.c
index e805e40799..885e000f9b 100644
--- a/monitor.c
+++ b/monitor.c
@@ -271,7 +271,10 @@ static QemuMutex monitor_lock;
 static GHashTable *monitor_qapi_event_state;
 static QTAILQ_HEAD(mon_list, Monitor) mon_list;
 
+/* Protects mon_fdsets */
+static QemuMutex mon_fdsets_lock;
 static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets;
+
 static int mon_refcount;
 
 static mon_cmd_t mon_cmds[];
@@ -2319,9 +2322,11 @@ static void monitor_fdsets_cleanup(void)
     MonFdset *mon_fdset;
     MonFdset *mon_fdset_next;
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH_SAFE(mon_fdset, &mon_fdsets, next, mon_fdset_next) {
         monitor_fdset_cleanup(mon_fdset);
     }
+    qemu_mutex_unlock(&mon_fdsets_lock);
 }
 
 AddfdInfo *qmp_add_fd(bool has_fdset_id, int64_t fdset_id, bool has_opaque,
@@ -2356,6 +2361,7 @@ void qmp_remove_fd(int64_t fdset_id, bool has_fd, int64_t fd, Error **errp)
     MonFdsetFd *mon_fdset_fd;
     char fd_str[60];
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
         if (mon_fdset->id != fdset_id) {
             continue;
@@ -2375,10 +2381,12 @@ void qmp_remove_fd(int64_t fdset_id, bool has_fd, int64_t fd, Error **errp)
             goto error;
         }
         monitor_fdset_cleanup(mon_fdset);
+        qemu_mutex_unlock(&mon_fdsets_lock);
         return;
     }
 
 error:
+    qemu_mutex_unlock(&mon_fdsets_lock);
     if (has_fd) {
         snprintf(fd_str, sizeof(fd_str), "fdset-id:%" PRId64 ", fd:%" PRId64,
                  fdset_id, fd);
@@ -2394,6 +2402,7 @@ FdsetInfoList *qmp_query_fdsets(Error **errp)
     MonFdsetFd *mon_fdset_fd;
     FdsetInfoList *fdset_list = NULL;
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
         FdsetInfoList *fdset_info = g_malloc0(sizeof(*fdset_info));
         FdsetFdInfoList *fdsetfd_list = NULL;
@@ -2423,6 +2432,7 @@ FdsetInfoList *qmp_query_fdsets(Error **errp)
         fdset_info->next = fdset_list;
         fdset_list = fdset_info;
     }
+    qemu_mutex_unlock(&mon_fdsets_lock);
 
     return fdset_list;
 }
@@ -2435,6 +2445,7 @@ AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,
     MonFdsetFd *mon_fdset_fd;
     AddfdInfo *fdinfo;
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     if (has_fdset_id) {
         QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
             /* Break if match found or match impossible due to ordering by ID */
@@ -2455,6 +2466,7 @@ AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,
             if (fdset_id < 0) {
                 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "fdset-id",
                            "a non-negative value");
+                qemu_mutex_unlock(&mon_fdsets_lock);
                 return NULL;
             }
             /* Use specified fdset ID */
@@ -2505,16 +2517,21 @@ AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,
     fdinfo->fdset_id = mon_fdset->id;
     fdinfo->fd = mon_fdset_fd->fd;
 
+    qemu_mutex_unlock(&mon_fdsets_lock);
     return fdinfo;
 }
 
 int monitor_fdset_get_fd(int64_t fdset_id, int flags)
 {
-#ifndef _WIN32
+#ifdef _WIN32
+    return -ENOENT;
+#else
     MonFdset *mon_fdset;
     MonFdsetFd *mon_fdset_fd;
     int mon_fd_flags;
+    int ret;
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
         if (mon_fdset->id != fdset_id) {
             continue;
@@ -2522,20 +2539,24 @@ int monitor_fdset_get_fd(int64_t fdset_id, int flags)
         QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
             mon_fd_flags = fcntl(mon_fdset_fd->fd, F_GETFL);
             if (mon_fd_flags == -1) {
-                return -1;
+                ret = -errno;
+                goto out;
             }
 
             if ((flags & O_ACCMODE) == (mon_fd_flags & O_ACCMODE)) {
-                return mon_fdset_fd->fd;
+                ret = mon_fdset_fd->fd;
+                goto out;
             }
         }
-        errno = EACCES;
-        return -1;
+        ret = -EACCES;
+        goto out;
     }
-#endif
+    ret = -ENOENT;
 
-    errno = ENOENT;
-    return -1;
+out:
+    qemu_mutex_unlock(&mon_fdsets_lock);
+    return ret;
+#endif
 }
 
 int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
@@ -2543,20 +2564,25 @@ int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
     MonFdset *mon_fdset;
     MonFdsetFd *mon_fdset_fd_dup;
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
         if (mon_fdset->id != fdset_id) {
             continue;
         }
         QLIST_FOREACH(mon_fdset_fd_dup, &mon_fdset->dup_fds, next) {
             if (mon_fdset_fd_dup->fd == dup_fd) {
-                return -1;
+                goto err;
             }
         }
         mon_fdset_fd_dup = g_malloc0(sizeof(*mon_fdset_fd_dup));
         mon_fdset_fd_dup->fd = dup_fd;
         QLIST_INSERT_HEAD(&mon_fdset->dup_fds, mon_fdset_fd_dup, next);
+        qemu_mutex_unlock(&mon_fdsets_lock);
         return 0;
     }
+
+err:
+    qemu_mutex_unlock(&mon_fdsets_lock);
     return -1;
 }
 
@@ -2565,6 +2591,7 @@ static int monitor_fdset_dup_fd_find_remove(int dup_fd, bool remove)
     MonFdset *mon_fdset;
     MonFdsetFd *mon_fdset_fd_dup;
 
+    qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
         QLIST_FOREACH(mon_fdset_fd_dup, &mon_fdset->dup_fds, next) {
             if (mon_fdset_fd_dup->fd == dup_fd) {
@@ -2573,13 +2600,17 @@ static int monitor_fdset_dup_fd_find_remove(int dup_fd, bool remove)
                     if (QLIST_EMPTY(&mon_fdset->dup_fds)) {
                         monitor_fdset_cleanup(mon_fdset);
                     }
-                    return -1;
+                    goto err;
                 } else {
+                    qemu_mutex_unlock(&mon_fdsets_lock);
                     return mon_fdset->id;
                 }
             }
         }
     }
+
+err:
+    qemu_mutex_unlock(&mon_fdsets_lock);
     return -1;
 }
 
@@ -4519,6 +4550,7 @@ void monitor_init_globals(void)
     monitor_qapi_event_init();
     sortcmdlist();
     qemu_mutex_init(&monitor_lock);
+    qemu_mutex_init(&mon_fdsets_lock);
     monitor_iothread_init();
 }
 
diff --git a/stubs/fdset.c b/stubs/fdset.c
index 6020cf28c8..4f3edf2ea4 100644
--- a/stubs/fdset.c
+++ b/stubs/fdset.c
@@ -14,7 +14,7 @@ int monitor_fdset_dup_fd_find(int dup_fd)
 
 int monitor_fdset_get_fd(int64_t fdset_id, int flags)
 {
-    return -1;
+    return -ENOENT;
 }
 
 void monitor_fdset_dup_fd_remove(int dupfd)
diff --git a/util/osdep.c b/util/osdep.c
index a73de0e1ba..ea51d500b6 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -302,7 +302,8 @@ int qemu_open(const char *name, int flags, ...)
         }
 
         fd = monitor_fdset_get_fd(fdset_id, flags);
-        if (fd == -1) {
+        if (fd < 0) {
+            errno = -fd;
             return -1;
         }
 
-- 
2.17.1

Re: [Qemu-devel] [PULL 0/7] monitor: Thread safety improvements

[Peter Maydell]

On 18 June 2018 at 15:08, Markus Armbruster <armbru@redhat.com> wrote:
> The following changes since commit 2ef2f16781af9dee6ba6517755e9073ba5799fa2:
>
>   Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20180615a' into staging (2018-06-15 18:13:35 +0100)
>
> are available in the Git repository at:
>
>   git://repo.or.cz/qemu/armbru.git tags/pull-monitor-2018-06-18
>
> for you to fetch changes up to 474514668b47c9d2148b526e379ffbb6764d9a9e:
>
>   monitor: add lock to protect mon_fdsets (2018-06-18 15:48:22 +0200)
>
> ----------------------------------------------------------------
> Monitor patches for 2018-06-18
>
> ----------------------------------------------------------------


Applied, thanks.

-- PMM