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Code Issues Releases Activity

pthread_frame: call update_context_from_user() after acquiring lock.

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Otherwise the thread may still be in the middle of decoding a previous
frame, which would effectively trigger a race condition on any field
concurrently read and written.

In practice, this fixes tsan warnings like the following:

WARNING: ThreadSanitizer: data race (pid=17380)
  Write of size 4 at 0x7d64000160fc by main thread:
    #0 update_context_from_user src/libavcodec/pthread_frame.c:335 (ffmpeg+0x000000dca515)
[..]
  Previous read of size 4 at 0x7d64000160fc by thread T2 (mutexes: write M1821):
    #0 ff_thread_report_progress src/libavcodec/pthread_frame.c:565 (ffmpeg+0x000000dcb08a)
This commit is contained in:
Ronald S. Bultje 2017-04-03 09:48:53 -04:00
parent 76d8c77430
commit 1269cd5b6f
1 changed files with 9 additions and 5 deletions
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14
libavcodec/pthread_frame.c
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@ -380,7 +380,8 @@ static void release_delayed_buffers(PerThreadContext *p)
}
}
static int submit_packet(PerThreadContext *p, AVPacket *avpkt)
static int submit_packet(PerThreadContext *p, AVCodecContext *user_avctx,
AVPacket *avpkt)
{
FrameThreadContext *fctx = p->parent;
PerThreadContext *prev_thread = fctx->prev_thread;
@ -392,6 +393,12 @@ static int submit_packet(PerThreadContext *p, AVPacket *avpkt)
pthread_mutex_lock(&p->mutex);
ret = update_context_from_user(p->avctx, user_avctx);
if (ret) {
pthread_mutex_unlock(&p->mutex);
return ret;
}
release_delayed_buffers(p);
if (prev_thread) {
@ -480,10 +487,7 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
*/
p = &fctx->threads[fctx->next_decoding];
err = update_context_from_user(p->avctx, avctx);
if (err)
goto finish;
err = submit_packet(p, avpkt);
err = submit_packet(p, avctx, avpkt);
if (err)
goto finish;