On Wed, Apr 08, 2015 at 11:37:52AM +0100, Stefan Hajnoczi wrote:
> > + QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
> > + AioContext *aio_context = bdrv_get_aio_context(bs);
> > +
> > + aio_context_acquire(aio_context);
> > + if (bs->job) {
> > + block_job_pause(bs->job);
> > + }
> > + aio_context_release(aio_context);
> > + }
> > +
> > while (busy) {
> > busy = false;
> >
> > @@ -2044,6 +2054,16 @@ void bdrv_drain_all(void)
> > aio_context_release(aio_context);
> > }
> > }
> > +
> > + QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
> > + AioContext *aio_context = bdrv_get_aio_context(bs);
> > +
> > + aio_context_acquire(aio_context);
> > + if (bs->job) {
> > + block_job_resume(bs->job);
> > + }
> > + aio_context_release(aio_context);
> > + }
> > }
>
> There is a tiny chance that we pause a job (which actually just sets
> job->paused = true but there's no guarantee the job's coroutine
> reacts to this) right before it terminates. Then aio_poll() enters
> the coroutine one last time and the job terminates.
>
> We then reach the resume portion of bdrv_drain_all() and the job no
> longer exists. Hopefully nothing started a new job in the meantime.
> bs->job should either be the original block job or NULL.
>
> This code seems under current assumptions, but I just wanted to
> raise these issues in case someone sees problems that I've missed.
Is it possible that a new job is started in the meantime? If that's
the case this will hit the assertion in block_job_resume().
Berto
