[FFmpeg-trac] #8643(avcodec:new): Data race in pthread_frame.c

[FFmpeg]

#8643: Data race in pthread_frame.c
-----------------------------------+-------------------------------------
             Reporter:  Zu-Ming    |                     Type:  defect
               Status:  new        |                 Priority:  important
            Component:  avcodec    |                  Version:  4.2
             Keywords:  Data race  |               Blocked By:
             Blocking:             |  Reproduced by developer:  0
Analyzed by developer:  0          |
-----------------------------------+-------------------------------------
 Summary of the bug:

 **Execute command: ** `./ffmpeg -y -threads 4 -i small.mp4 output.avi`

 **Version:** 4.2

 **Race object:** `p->result`

 **Thread 1:**

 **Access:** `p->result = codec->decode(avctx, p->frame, &p->got_frame,
 &p->avpkt);`

 **Line number:** `pthread_frame.c; 201`

 **Call stack:**

 1. `frame_worker_thread()`

 **Lock:** `pthread_mutex_lock(&p->mutex);`

 **Thread 2:**

 **Access:** `p->result = 0;`

 **Line number:** `h264dec.c; 913`

 **Call stack:**

 1. `ff_thread_decode_frame()`
 2. `decode_simple_internal()`
 3. `decode_simple_receive_frame()`
 4. `decode_receive_frame_internal()`
 5. `avcodec_send_packet()`
 6. `decode()`
 7. `decode_video()`
 8. `process_input_packet()`
 9. `transcode()`
 10. `main()`

 **Lock:** None

 **Impact:** This race cause `p->result` uncertain, which may affect the
 status of ffmpeg.

 My data race fuzzer, conzzer, finds that these 2 accesses can be executed
 concurrently, and they are protected by different locks, so my fuzzer
 report this race.

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Ticket URL: <https://trac.ffmpeg.org/ticket/8643>
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