Re: [Qemu-block] [PATCH] migration: re-active images while migration been canceled after inactive them

[Hailiang Zhang]

On 2017/1/23 21:40, Dr. David Alan Gilbert wrote:
> * zhanghailiang (address@hidden) wrote:
> > commit fe904ea8242cbae2d7e69c052c754b8f5f1ba1d6 fixed a case
> > which migration aborted QEMU because it didn't regain the control
> > of images while some errors happened.
> >
> > Actually, there are another two cases can trigger the same error reports:
> > " bdrv_co_do_pwritev: Assertion `!(bs->open_flags & 0x0800)' failed",
> >
> > Case 1, codes path:
> > migration_thread()
> >      migration_completion()
> >          bdrv_inactivate_all() ----------------> inactivate images
> >          qemu_savevm_state_complete_precopy()
> >              socket_writev_buffer() --------> error because destination fails
> >                  qemu_fflush() -------------------> set error on migration 
> > stream
> > -> qmp_migrate_cancel() ---------------------> user cancelled migration 
> > concurrently
> >      -> migrate_set_state() ------------------> set migrate CANCELLIN
> >      migration_completion() -----------------> go on to fail_invalidate
> >         if (s->state == MIGRATION_STATUS_ACTIVE) -> Jump this branch
> >
> > Case 2, codes path:
> > migration_thread()
> >      migration_completion()
> >          bdrv_inactivate_all() ----------------> inactivate images
> >      migreation_completion() finished
> > -> qmp_migrate_cancel() ---------------------> user cancelled migration 
> > concurrently
> >      qemu_mutex_lock_iothread();
> >      qemu_bh_schedule (s->cleanup_bh);
> >
> > As we can see from above, qmp_migrate_cancel can slip in whenever
> > migration_thread does not hold the global lock. If this happens after
> > bdrv_inactive_all() been called, the above error reports will appear.
> >
> > To prevent this, we can call bdrv_invalidate_cache_all() in qmp_migrate_cancel()
> > directly if we find images become inactive.
> >
> > Signed-off-by: zhanghailiang <address@hidden>
> > ---
> > Hi,
> >
> > I have sent another patch before to fix this problem, but didn't cover
> > all the scenes, and there are some discussions about this problem,
> > For more detail, please refer to
> > https://lists.gnu.org/archive/html/qemu-block/2016-12/msg00003.html
> > ---
> >   include/migration/migration.h |  3 +++
> >   migration/migration.c         | 13 +++++++++++++
> >   2 files changed, 16 insertions(+)
> >
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index c309d23..2d5b724 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -177,6 +177,9 @@ struct MigrationState
> >       /* Flag set once the migration thread is running (and needs joining) */
> >       bool migration_thread_running;
> >
> > +    /* Flag set once the migration thread called bdrv_inactivate_all */
> > +    bool block_inactive;
> > +
> >       /* Queue of outstanding page requests from the destination */
> >       QemuMutex src_page_req_mutex;
> >       QSIMPLEQ_HEAD(src_page_requests, MigrationSrcPageRequest) 
> > src_page_requests;
> > diff --git a/migration/migration.c b/migration/migration.c
> > index f498ab8..9defb3e 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1006,6 +1006,16 @@ static void migrate_fd_cancel(MigrationState *s)
> >       if (s->state == MIGRATION_STATUS_CANCELLING && f) {
> >           qemu_file_shutdown(f);
> >       }
> > +    if (s->state == MIGRATION_STATUS_CANCELLING && s->block_inactive) {
> > +        Error *local_err = NULL;
> > +
> > +        bdrv_invalidate_cache_all(&local_err);
> > +        if (local_err) {
> > +            error_report_err(local_err);
> > +        } else {
> > +            s->block_inactive = false;
> > +        }
> > +    }
> >   }
> >
> >   void add_migration_state_change_notifier(Notifier *notify)
> > @@ -1705,6 +1715,7 @@ static void migration_completion(MigrationState *s, int 
> > current_active_state,
> >               if (ret >= 0) {
> >                   qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX);
> >                   qemu_savevm_state_complete_precopy(s->to_dst_file, false);
> > +                s->block_inactive = true;
> >               }
> >           }
> >           qemu_mutex_unlock_iothread();
> > @@ -1758,6 +1769,8 @@ fail_invalidate:
> >           bdrv_invalidate_cache_all(&local_err);
> >           if (local_err) {
> >               error_report_err(local_err);
> > +        } else {
> > +            s->block_inactive = false;
> >           }
>
> I think the fe904 commit also add the problem that this 
> bdrv_invalidate_cache_all
> is done outside the big lock (Stefan and Kevin tell me bdrv_* calls generally
> need the lock).

Ha, you are right, I didn't noticed that all the time.
So should I just add the big lock there ? Is that enough?

Thanks,
Hailiang

> Dave
>
> >       }
> >
> > --
> > 1.8.3.1
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>
> .