[PATCH 3/5] amstream: Add a second critical section for filter methods that are called from streams.

[Anton Baskanov]

On четверг, 8 апреля 2021 г. 22:12:35 +07 you wrote:
> On 4/8/21 1:14 AM, Anton Baskanov wrote:
> > On среда, 7 апреля 2021 г. 22:27:33 
+07 you wrote:
> >> On 4/6/21 1:04 PM, Anton Baskanov wrote:
> >>> Signed-off-by: Anton Baskanov <baskanov at gmail.com>
> >>> ---
> >>> This is required to avoid deadlocks, e.g. when the filter is stopped
> >>> while EndOfStream is being called.
> >> 
> >> So, if I understand correctly, the race is:
> >> 
> >> 
> >> Main thread			Streaming thread
> >> ------------------------------------------------
> >> IMediaControl::Stop()		IPin::EndOfStream()
> >> lock graph->cs		IMediaStreamFilter::EndOfStream()
> >> stop parser filter
> >> wait for streaming thread	try to grab graph->cs
> >> 
> >> 
> >> Shouldn't patch 0005 be enough to avoid this? We don't hold filter->cs,
> >> or any amstream-specific locks, while waiting for streaming threads to
> >> stop.> 
> > Actually, the deadlock is:
> > 
> > Main thread			Streaming thread
> > ------------------------------------------------
> > IMediaStreamFilter::Stop()		IPin::EndOfStream()
> > lock filter->cs		lock stream->cs
> > IAMMediaStream::SetState()	IMediaStreamFilter::EndOfStream()
> > try to lock stream->cs		try to lock filter->cs
> > 
> > In theory, it should be possible to move SetState() calls out of the
> > filter
> > critical section, but there are other possible deadlocks, like:
> > 
> > Main thread			Streaming thread
> > ------------------------------------------------
> > IMediaStreamFilter::GetStopPosition()	IPin::EndOfStream()
> > lock filter->cs		lock stream->cs
> > get_seeking()
> > IPin_ConnectedTo()		IMediaStreamFilter::EndOfStream()
> > try to lock stream->cs		try to lock filter->cs
> 
> Ah. Yeah, lock ordering would be a problem. Fortunately it only seems to
> be a problem there.
> 
> Could we instead call IMediaStreamFilter::EndOfStream() not inside
> stream->cs? That solution seems potentially simpler, judging by your
> not-yet-submitted commit 4ad440dde6. It should probably be accompanied
> by a comment; probably we should add a similar comment to
> IStreamSample::GetSampleTimes().

Looks like this should work. There will be a race condition where 
IMediaStreamFilter::Flush is called before MediaStreamFilter::EndOfStream. 
AFAICS this should not cause any issues other than making eos_count negative 
briefly.