Re: [Qemu-devel] [PATCH v3] mirror: Confirm we're quiesced only if the job is paused or cancelled

[Kevin Wolf]

Am 08.03.2019 um 16:48 hat Sergio Lopez geschrieben:
> While child_job_drained_begin() calls to job_pause(), the job doesn't
> actually transition between states until it runs again and reaches a
> pause point. This means bdrv_drained_begin() may return with some jobs
> using the node still having 'busy == true'.
> 
> As a consequence, block_job_detach_aio_context() may get into a
> deadlock, waiting for the job to be actually paused, while the coroutine
> servicing the job is yielding and doesn't get the opportunity to get
> scheduled again. This situation can be reproduced by issuing a
> 'block-commit' immediately followed by a 'device_del'.
> 
> To ensure bdrv_drained_begin() only returns when the jobs have been
> paused, we change mirror_drained_poll() to only confirm it's quiesced
> when job->paused == true and there aren't any in-flight requests, except
> if we reached that point by a drained section initiated by the
> mirror/commit job itself.
> 
> The other block jobs shouldn't need any changes, as the default
> drained_poll() behavior is to only confirm it's quiesced if the job is
> not busy or completed.
> 
> Signed-off-by: Sergio Lopez <address@hidden>

Thanks, applied to the block branch.

Kevin