[Webkit-unassigned] [Bug 260067] New: [MSE][GStreamer] Deadlock while flushing on paused when there's a non in-place transform element

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=260067

            Bug ID: 260067
           Summary: [MSE][GStreamer] Deadlock while flushing on paused
                    when there's a non in-place transform element
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: eocanha at igalia.com

There is a deadlock possible inside WebKit media src (MSE) between streaming thread handling CAPS event and pipeline flush in the main thread. This happens in case where there is a transform element in the pipeline that does transition NOT in place. Basetransform elem expects that it will allocate buffers so on CAPS change it triggers allocation negotiations (ALLOCATION query). In such case CAPS event becomes fully synchronous as basetransform does ALLOCATION query that is synchronous (serialized with data) and may block the streaming thread. If the pipeline is paused and the sink thread doesn't accept any data, this will block CAPS event until pipeline is unpaused or flushed. But flush requires a lock that streaming thread is holding (DataMutexLocker streamingMembers { stream->streamingMembersDataMutex };)

See: https://github.com/WebPlatformForEmbedded/WPEWebKit/issues/1135

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