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)
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