On 06/10/17 20:53, Mark Thompson wrote:
> On 06/10/17 08:52, Jorge Ramirez-Ortiz wrote:
>> It occurs when the codec is closed while buffer references still
>> exist. This is a regression from the original patchset where support
>> for this use-case was implemented.
>>
>> The regression occurred while cleaning the code for the last patchset
>> (decoding was tested only with ffplay which disposes of the buffer
>> straightaway hence the feature went in broken/untested)
>> ---
>> libavcodec/v4l2_m2m.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/libavcodec/v4l2_m2m.c b/libavcodec/v4l2_m2m.c
>> index bd96a6d..5e85bcb 100644
>> --- a/libavcodec/v4l2_m2m.c
>> +++ b/libavcodec/v4l2_m2m.c
>> @@ -331,8 +331,10 @@ int ff_v4l2_m2m_codec_end(AVCodecContext *avctx)
>>
>> ff_v4l2_context_release(&s->output);
>>
>> - if (atomic_load(&s->refcount))
>> - av_log(avctx, AV_LOG_ERROR, "ff_v4l2m2m_codec_end leaving pending
>> buffers\n");
>> + if (atomic_load(&s->refcount)) {
>> + av_log(avctx, AV_LOG_DEBUG, "ff_v4l2m2m_codec_end leaving pending
>> buffers\n");
>> + return 0;
>> + }
>>
>> ff_v4l2_context_release(&s->capture);
>> sem_destroy(&s->refsync);
>>
>
> Trying to test this, I segfault when decoding finishes with this patch
> applied (exynos s5p-mfc):
>
> (gdb) r
> Starting program: /home/mrt/ffmpeg/v4l2/build/ffmpeg_g -threads 1 -v 55 -y
> -c:v h264_v4l2m2m -i /home/mrt/bbb_1080_264.mp4 -an -frames:v 100 -f null -
> ...
> Output file #0 (pipe:):
> Output stream #0:0 (video): 100 frames encoded; 100 packets muxed (40000
> bytes);
> Total: 100 packets (40000 bytes) muxed
> [h264_v4l2m2m @ 0x1403720] ff_v4l2m2m_codec_end leaving pending buffers
> 100 frames successfully decoded, 0 decoding errors
> ...
> Thread 1 "ffmpeg_g" received signal SIGSEGV, Segmentation fault.
> ff_v4l2_context_set_status (ctx=ctx@entry=0x10fc, cmd=1074026003) at
> src/libavcodec/v4l2_context.c:489
> 489 int type = ctx->type;
> (gdb) bt
> #0 ff_v4l2_context_set_status (ctx=ctx@entry=0x10fc, cmd=1074026003) at
> src/libavcodec/v4l2_context.c:489
> #1 0x00798c24 in ff_v4l2_m2m_codec_end (avctx=0x1403720) at
> src/libavcodec/v4l2_m2m.c:319
> #2 0x00835aba in buffer_replace (src=0x0, dst=<optimized out>) at
> src/libavutil/buffer.c:120
> #3 av_buffer_unref (buf=buf@entry=0x14d8b2c) at src/libavutil/buffer.c:130
> #4 0x008417ac in av_frame_unref (frame=frame@entry=0x14d8a30) at
> src/libavutil/frame.c:515
> #5 0x00841d58 in av_frame_unref (frame=<optimized out>) at
> src/libavutil/frame.c:147
> #6 av_frame_free (frame=frame@entry=0x1403d9c) at src/libavutil/frame.c:168
> #7 0x00082bce in ffmpeg_cleanup (ret=0) at src/fftools/ffmpeg.c:541
> #8 0x00079c42 in exit_program (ret=0) at src/fftools/cmdutils.c:138
> #9 0x0006efba in main (argc=<optimized out>, argv=<optimized out>) at
> src/fftools/ffmpeg.c:4793
> (gdb) p ctx
> $1 = (V4L2Context *) 0x10fc
> (gdb) f 1
> #1 0x00798c24 in ff_v4l2_m2m_codec_end (avctx=0x1403720) at
> src/libavcodec/v4l2_m2m.c:319
> 319 ret = ff_v4l2_context_set_status(&s->output, VIDIOC_STREAMOFF);
> (gdb) p s
> $2 = (V4L2m2mContext *) 0x0
> (gdb)
>
To clarify, it segfaults in the same way without the patch as well.
- Mark
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