Hi,
I'd like to report a tsan warning about a data race in the h264 decoder.
1. Steps to reproduce:
./configure --samples=~/fate-suite/ --toolchain=clang-tsan --disable-stripping
make fate-h264 THREADS=4
2. Here is an excerpt of the tsan warning in
tests/data/fate/h264-conformance-ba1_ft_c.err:
WARNING: ThreadSanitizer: data race (pid=31070)
Write of size 8 at 0x7bbc000082a8 by thread T1 (mutexes: write M1628):
#0 memcpy
/work/release-test/final/llvm.src/projects/compiler-rt/lib/tsan/../sanitizer_common/sanitizer_common_interceptors.inc:655:5
(ffmpeg+0x10de9d)
#1 h264_initialise_ref_list
home/wtc/tmp/ffmpeg/libavcodec/h264_refs.c:214:29 (ffmpeg+0x1186b3f)
#2 ff_h264_build_ref_list
home/wtc/tmp/ffmpeg/libavcodec/h264_refs.c:306 (ffmpeg+0x1186b3f)
#3 h264_slice_init
home/wtc/tmp/ffmpeg/libavcodec/h264_slice.c:1900:11 (ffmpeg+0x1191149)
#4 ff_h264_queue_decode_slice
home/wtc/tmp/ffmpeg/libavcodec/h264_slice.c:2129 (ffmpeg+0x1191149)
#5 decode_nal_units
home/wtc/tmp/ffmpeg/libavcodec/h264dec.c:675:24 (ffmpeg+0x7924ec)
#6 h264_decode_frame home/wtc/tmp/ffmpeg/libavcodec/h264dec.c:1006
(ffmpeg+0x7924ec)
#7 frame_worker_thread
home/wtc/tmp/ffmpeg/libavcodec/pthread_frame.c:201:21
(ffmpeg+0xae56dc)
Previous read of size 8 at 0x7bbc000082a8 by main thread (mutexes:
write M1630):
#0 memcpy
/work/release-test/final/llvm.src/projects/compiler-rt/lib/tsan/../sanitizer_common/sanitizer_common_interceptors.inc:655:5
(ffmpeg+0x10de9d)
#1 ff_h264_update_thread_context
home/wtc/tmp/ffmpeg/libavcodec/h264_slice.c:411:5 (ffmpeg+0x118b7dc)
#2 update_context_from_thread
home/wtc/tmp/ffmpeg/libavcodec/pthread_frame.c:315:19
(ffmpeg+0xae4302)
#3 submit_packet
home/wtc/tmp/ffmpeg/libavcodec/pthread_frame.c:418:15
(ffmpeg+0xae3783)
#4 ff_thread_decode_frame
home/wtc/tmp/ffmpeg/libavcodec/pthread_frame.c:495 (ffmpeg+0xae3783)
#5 decode_simple_internal
home/wtc/tmp/ffmpeg/libavcodec/decode.c:415:15 (ffmpeg+0x665ae4)
#6 decode_simple_receive_frame
home/wtc/tmp/ffmpeg/libavcodec/decode.c:620 (ffmpeg+0x665ae4)
#7 decode_receive_frame_internal
home/wtc/tmp/ffmpeg/libavcodec/decode.c:638 (ffmpeg+0x665ae4)
#8 avcodec_send_packet
home/wtc/tmp/ffmpeg/libavcodec/decode.c:678:15 (ffmpeg+0x665017)
#9 decode home/wtc/tmp/ffmpeg/ffmpeg.c:2265:15 (ffmpeg+0x1a748e)
#10 decode_video home/wtc/tmp/ffmpeg/ffmpeg.c:2409 (ffmpeg+0x1a748e)
#11 process_input_packet home/wtc/tmp/ffmpeg/ffmpeg.c:2644
(ffmpeg+0x1a748e) #12 process_input
home/wtc/tmp/ffmpeg/ffmpeg.c:4432:5 (ffmpeg+0x1a2e69)
#13 transcode_step home/wtc/tmp/ffmpeg/ffmpeg.c:4543 (ffmpeg+0x1a2e69)
#14 transcode home/wtc/tmp/ffmpeg/ffmpeg.c:4597 (ffmpeg+0x1a2e69)
#15 main home/wtc/tmp/ffmpeg/ffmpeg.c:4803:9 (ffmpeg+0x19daef)
3. The relevant source code is:
libavcodec/h264_refs.c:
135 static void h264_initialise_ref_list(H264Context *h, H264SliceContext *sl)
136 {
...
213 for (i = 0; i < sl->list_count; i++)
214 h->default_ref[i] = sl->ref_list[i][0];
215 }
libavcodec/h264_slice.c:
288 int ff_h264_update_thread_context(AVCodecContext *dst,
289 const AVCodecContext *src)
290 {
...
409 memcpy(&h->poc, &h1->poc, sizeof(h->poc));
410
411 memcpy(h->default_ref, h1->default_ref, sizeof(h->default_ref));
412 memcpy(h->short_ref, h1->short_ref, sizeof(h->short_ref));
413 memcpy(h->long_ref, h1->long_ref, sizeof(h->long_ref));
414 memcpy(h->delayed_pic, h1->delayed_pic, sizeof(h->delayed_pic));
415 memcpy(h->last_pocs, h1->last_pocs, sizeof(h->last_pocs));
4. I can eliminate the tsan warning by deleting line 411 in
libavcodec/h264_slice.c, but I don't know if that is the correct fix.
diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index 6deb08fe6d..2fb89b189d 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -408,7 +408,6 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
memcpy(&h->poc, &h1->poc, sizeof(h->poc));
- memcpy(h->default_ref, h1->default_ref, sizeof(h->default_ref));
memcpy(h->short_ref, h1->short_ref, sizeof(h->short_ref));
memcpy(h->long_ref, h1->long_ref, sizeof(h->long_ref));
memcpy(h->delayed_pic, h1->delayed_pic, sizeof(h->delayed_pic));
Wan-Teh Chang
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