Re: [PATCH v4 10/25] migration: Add Error** argument to qemu_savevm_state_setup()

["Cédric Le Goater" <clg@redhat.com>]

On 3/8/24 13:56, Peter Xu wrote:
> On Wed, Mar 06, 2024 at 02:34:25PM +0100, Cédric Le Goater wrote:
>> This prepares ground for the changes coming next which add an Error**
>> argument to the .save_setup() handler. Callers of qemu_savevm_state_setup()
>> now handle the error and fail earlier setting the migration state from
>> MIGRATION_STATUS_SETUP to MIGRATION_STATUS_FAILED.
>>
>> In qemu_savevm_state(), move the cleanup to preserve the error
>> reported by .save_setup() handlers.
>>
>> Since the previous behavior was to ignore errors at this step of
>> migration, this change should be examined closely to check that
>> cleanups are still correctly done.
>>
>> Signed-off-by: Cédric Le Goater <clg@redhat.com>
>> ---
>>
>>   Changes in v4:
>>   
>>   - Merged cleanup change in qemu_savevm_state()
>>     
>>   Changes in v3:
>>   
>>   - Set migration state to MIGRATION_STATUS_FAILED
>>   - Fixed error handling to be done under lock in bg_migration_thread()
>>   - Made sure an error is always set in case of failure in
>>     qemu_savevm_state_setup()
>>     
>>   migration/savevm.h    |  2 +-
>>   migration/migration.c | 27 ++++++++++++++++++++++++---
>>   migration/savevm.c    | 26 +++++++++++++++-----------
>>   3 files changed, 40 insertions(+), 15 deletions(-)
>>
>> diff --git a/migration/savevm.h b/migration/savevm.h
>> index 74669733dd63a080b765866c703234a5c4939223..9ec96a995c93a42aad621595f0ed58596c532328 100644
>> --- a/migration/savevm.h
>> +++ b/migration/savevm.h
>> @@ -32,7 +32,7 @@
>>   bool qemu_savevm_state_blocked(Error **errp);
>>   void qemu_savevm_non_migratable_list(strList **reasons);
>>   int qemu_savevm_state_prepare(Error **errp);
>> -void qemu_savevm_state_setup(QEMUFile *f);
>> +int qemu_savevm_state_setup(QEMUFile *f, Error **errp);
>>   bool qemu_savevm_state_guest_unplug_pending(void);
>>   int qemu_savevm_state_resume_prepare(MigrationState *s);
>>   void qemu_savevm_state_header(QEMUFile *f);
>> diff --git a/migration/migration.c b/migration/migration.c
>> index a49fcd53ee19df1ce0182bc99d7e064968f0317b..6d1544224e96f5edfe56939a9c8395d88ef29581 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -3408,6 +3408,8 @@ static void *migration_thread(void *opaque)
>>       int64_t setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
>>       MigThrError thr_error;
>>       bool urgent = false;
>> +    Error *local_err = NULL;
>> +    int ret;
>>   
>>       thread = migration_threads_add("live_migration", qemu_get_thread_id());
>>   
>> @@ -3451,9 +3453,17 @@ static void *migration_thread(void *opaque)
>>       }
>>   
>>       bql_lock();
>> -    qemu_savevm_state_setup(s->to_dst_file);
>> +    ret = qemu_savevm_state_setup(s->to_dst_file, &local_err);
>>       bql_unlock();
>>   
>> +    if (ret) {
>> +        migrate_set_error(s, local_err);
>> +        error_free(local_err);
>> +        migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
>> +                          MIGRATION_STATUS_FAILED);
>> +        goto out;
>> +     }
> 
> There's a small indent issue, I can fix it.

checkpatch did report anything.

> 
> The bigger problem is I _think_ this will trigger a ci failure in the
> virtio-net-failover test:
> 
> ▶ 121/464 ERROR:../tests/qtest/virtio-net-failover.c:1203:test_migrate_abort_wait_unplug: assertion failed (status == "cancelling"): ("cancelled" == "cancelling") ERROR
> 121/464 qemu:qtest+qtest-x86_64 / qtest-x86_64/virtio-net-failover    ERROR            4.77s   killed by signal 6 SIGABRT
>>>> PYTHON=/builds/peterx/qemu/build/pyvenv/bin/python3.8 G_TEST_DBUS_DAEMON=/builds/peterx/qemu/tests/dbus-vmstate-daemon.sh MALLOC_PERTURB_=161 QTEST_QEMU_IMG=./qemu-img QTEST_QEMU_STORAGE_DAEMON_BINARY=./storage-daemon/qemu-storage-daemon QTEST_QEMU_BINARY=./qemu-system-x86_64 /builds/peterx/qemu/build/tests/qtest/virtio-net-failover --tap -k
> ――――――――――――――――――――――――――――――――――――― ✀  ―――――――――――――――――――――――――――――――――――――
> stderr:
> qemu-system-x86_64: ram_save_setup failed: Input/output error
> **
> ERROR:../tests/qtest/virtio-net-failover.c:1203:test_migrate_abort_wait_unplug: assertion failed (status == "cancelling"): ("cancelled" == "cancelling")
> (test program exited with status code -6)
> ――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
> 
> I am not familiar enough with the failover code, and may not have time
> today to follow this up, copy Laurent.  Cedric, if you have time, please
> have a look.  


Sure. Weird because I usually run make check on x86_64, s390x, ppc64 and
aarch64. Let me check again.


Thanks,

C.



> I'll give it a shot on Monday to find a solution, otherwise
> we may need to postpone some of the patches to 9.1.
> 
> Thanks,
> 
>> +
>>       qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
>>                                  MIGRATION_STATUS_ACTIVE);
>>   
>> @@ -3530,6 +3540,9 @@ static void *bg_migration_thread(void *opaque)
>>       MigThrError thr_error;
>>       QEMUFile *fb;
>>       bool early_fail = true;
>> +    bool setup_fail = true;
>> +    Error *local_err = NULL;
>> +    int ret;
>>   
>>       rcu_register_thread();
>>       object_ref(OBJECT(s));
>> @@ -3563,9 +3576,16 @@ static void *bg_migration_thread(void *opaque)
>>   
>>       bql_lock();
>>       qemu_savevm_state_header(s->to_dst_file);
>> -    qemu_savevm_state_setup(s->to_dst_file);
>> +    ret = qemu_savevm_state_setup(s->to_dst_file, &local_err);
>> +    if (ret) {
>> +        migrate_set_error(s, local_err);
>> +        error_free(local_err);
>> +        goto fail;
>> +    }
>>       bql_unlock();
>>   
>> +    setup_fail = false;
>> +
>>       qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
>>                                  MIGRATION_STATUS_ACTIVE);
>>   
>> @@ -3632,7 +3652,8 @@ static void *bg_migration_thread(void *opaque)
>>   
>>   fail:
>>       if (early_fail) {
>> -        migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
>> +        migrate_set_state(&s->state,
>> +                setup_fail ? MIGRATION_STATUS_SETUP : MIGRATION_STATUS_ACTIVE,
>>                   MIGRATION_STATUS_FAILED);
>>           bql_unlock();
>>       }
>> diff --git a/migration/savevm.c b/migration/savevm.c
>> index ee31ffb5e88cea723039c754c30ce2c8a0ef35f3..63fdbb5ad7d4dbfaef1d2094350bf302cc677602 100644
>> --- a/migration/savevm.c
>> +++ b/migration/savevm.c
>> @@ -1310,11 +1310,11 @@ int qemu_savevm_state_prepare(Error **errp)
>>       return 0;
>>   }
>>   
>> -void qemu_savevm_state_setup(QEMUFile *f)
>> +int qemu_savevm_state_setup(QEMUFile *f, Error **errp)
>>   {
>> +    ERRP_GUARD();
>>       MigrationState *ms = migrate_get_current();
>>       SaveStateEntry *se;
>> -    Error *local_err = NULL;
>>       int ret = 0;
>>   
>>       json_writer_int64(ms->vmdesc, "page_size", qemu_target_page_size());
>> @@ -1323,10 +1323,9 @@ void qemu_savevm_state_setup(QEMUFile *f)
>>       trace_savevm_state_setup();
>>       QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
>>           if (se->vmsd && se->vmsd->early_setup) {
>> -            ret = vmstate_save(f, se, ms->vmdesc, &local_err);
>> +            ret = vmstate_save(f, se, ms->vmdesc, errp);
>>               if (ret) {
>> -                migrate_set_error(ms, local_err);
>> -                error_report_err(local_err);
>> +                migrate_set_error(ms, *errp);
>>                   qemu_file_set_error(f, ret);
>>                   break;
>>               }
>> @@ -1346,18 +1345,19 @@ void qemu_savevm_state_setup(QEMUFile *f)
>>           ret = se->ops->save_setup(f, se->opaque);
>>           save_section_footer(f, se);
>>           if (ret < 0) {
>> +            error_setg(errp, "failed to setup SaveStateEntry with id(name): "
>> +                       "%d(%s): %d", se->section_id, se->idstr, ret);
>>               qemu_file_set_error(f, ret);
>>               break;
>>           }
>>       }
>>   
>>       if (ret) {
>> -        return;
>> +        return ret;
>>       }
>>   
>> -    if (precopy_notify(PRECOPY_NOTIFY_SETUP, &local_err)) {
>> -        error_report_err(local_err);
>> -    }
>> +    /* TODO: Should we check that errp is set in case of failure ? */
>> +    return precopy_notify(PRECOPY_NOTIFY_SETUP, errp);
>>   }
>>   
>>   int qemu_savevm_state_resume_prepare(MigrationState *s)
>> @@ -1728,7 +1728,10 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
>>       ms->to_dst_file = f;
>>   
>>       qemu_savevm_state_header(f);
>> -    qemu_savevm_state_setup(f);
>> +    ret = qemu_savevm_state_setup(f, errp);
>> +    if (ret) {
>> +        goto cleanup;
>> +    }
>>   
>>       while (qemu_file_get_error(f) == 0) {
>>           if (qemu_savevm_state_iterate(f, false) > 0) {
>> @@ -1741,10 +1744,11 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
>>           qemu_savevm_state_complete_precopy(f, false, false);
>>           ret = qemu_file_get_error(f);
>>       }
>> -    qemu_savevm_state_cleanup();
>>       if (ret != 0) {
>>           error_setg_errno(errp, -ret, "Error while writing VM state");
>>       }
>> +cleanup:
>> +    qemu_savevm_state_cleanup();
>>   
>>       if (ret != 0) {
>>           status = MIGRATION_STATUS_FAILED;
>> -- 
>> 2.44.0
>>
>