#824: Segfault while using h264 hardware acceleration -------------------------------------+------------------------------------- Reporter: static-void | Type: defect Status: new | Priority: normal Component: avcodec | Version: git- Keywords: | master Blocking: | Blocked By: Analyzed by developer: 0 | Reproduced by developer: 0 -------------------------------------+------------------------------------- I'm using FFmpeg integrated in mplayer (with VA-API pathes), and I'm getting a SIGSEGV while trying to watch h264 video with HW-acceleration. I've poked around with gdb and I think this is multithreading-related. After I added mplayer option "-lavdopts threads=1", which configures libavcodec, the problem has gone. === General info === Crash happens inside a thread, in the start_frame function (libavcodec/vaapi_h264.c:234): {{{ vactx->slice_param_size = sizeof(VASliceParameterBufferH264); ^-- vactx is NULL }}} and vactx is AVCodecContext.hwaccel_context, which should be set to vaapi_context struct instance. But I've set a breakpoint and seen hwaccel_context being properly set at the init stage, although AVCodecContext pointer being not the same as the one in the place it crashes. I suppose it happens because AVCodecContext gets copied and its fields are replicated across worker threads (libavcodec/pthread.c), and I haven't seen hwaccel_context being copied in the code. Considering all above, I don't think it is needed to copy hwaccel_context, but rather to force threads=1 configuration on libavcodec when using HW acceleration. Several working threads would not improve anything in the case of HW accel, would they? === Debug info === {{{ (gdb) run -vo vaapi:gl -va vaapi "<...>.mkv" Starting program: /usr/local/mplayer-vaapi-build/mplayer -vo vaapi:gl -va vaapi "<...>.mkv" [Thread debugging using libthread_db enabled] MPlayer SVN-r34365-4.6.1 (C) 2000-2011 MPlayer Team Playing <...>.mkv. libavformat file format detected. [matroska,webm @ 0xc798e0]max_analyze_duration 5000000 reached at 5019000 [lavf] stream 0: video (h264), -vid 0 [lavf] stream 1: audio (aac), -aid 0, -alang jpn [lavf] stream 2: subtitle (ass), -sid 0, -slang eng VIDEO: [H264] 1280x720 0bpp 23.976 fps 0.0 kbps ( 0.0 kbyte/s) Load subtitles in <...> [vo_vaapi] Using OpenGL rendering libva: libva version 0.32.0 Xlib: extension "XFree86-DRI" missing on display ":0.0". libva: va_getDriverName() returns 0 libva: Trying to open /usr/lib/dri/fglrx_drv_video.so libva: va_openDriver() returns 0 Opening video filter: [ass auto=1] Couldn't open video filter 'ass'. ASS: cannot add video filter ========================================================================== Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family [New Thread 0x7fffe13b6700 (LWP 12803)] [New Thread 0x7fffe0bb5700 (LWP 12804)] Selected video codec: [ffh264] vfm: ffmpeg (FFmpeg H.264) ========================================================================== ========================================================================== Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders AUDIO: 48000 Hz, 2 ch, s16le, 0.0 kbit/0.00% (ratio: 0->192000) Selected audio codec: [ffaac] afm: ffmpeg (FFmpeg AAC (MPEG-2/MPEG-4 Audio)) ========================================================================== [AO SDL] Samplerate: 48000Hz Channels: Stereo Format s16le [New Thread 0x7fffdc3b3700 (LWP 12805)] [Thread 0x7fffdc3b3700 (LWP 12805) exited] [New Thread 0x7fffdc3b3700 (LWP 12806)] AO: [sdl] 48000Hz 2ch s16le (2 bytes per sample) Starting playback... Unsupported PixelFormat 61 [VD_FFMPEG] Trying pixfmt=1. Movie-Aspect is 1.78:1 - prescaling to correct movie aspect. VO: [vaapi] 1280x720 => 1280x720 H.264 VA-API Acceleration [VD_FFMPEG] XVMC-accelerated MPEG-2. Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7fffe13b6700 (LWP 12803)] start_frame (avctx=0x1b098c0, buffer=0x0, size=0) at libavcodec/vaapi_h264.c:234 234 vactx->slice_param_size = sizeof(VASliceParameterBufferH264); (gdb) bt #0 start_frame (avctx=0x1b098c0, buffer=0x0, size=0) at libavcodec/vaapi_h264.c:234 #1 0x00000000008724bb in decode_nal_units (h=0x2504250, buf=0x1b1b780 "", buf_size=2752) at libavcodec/h264.c:3920 #2 0x0000000000872c4a in decode_frame (avctx=0x1b098c0, data=0x1e53080, data_size=0x1e53200, avpkt=<optimized out>) at libavcodec/h264.c:4105 #3 0x0000000000945818 in frame_worker_thread (arg=0x1e52f20) at libavcodec/pthread.c:364 #4 0x00007ffff6170efc in start_thread () from /lib/x86_64-linux- gnu/libpthread.so.0 #5 0x00007ffff055389d in clone () from /lib/x86_64-linux-gnu/libc.so.6 #6 0x0000000000000000 in ?? () (gdb) disass /m $pc-32,+64 Dump of assembler code from 0x9af3a7 to 0x9af3e7: 225 { 0x00000000009af3ad <start_frame+0>: push %r14 0x00000000009af3af <start_frame+2>: push %r13 0x00000000009af3b1 <start_frame+4>: push %r12 0x00000000009af3b3 <start_frame+6>: push %rbp 0x00000000009af3b4 <start_frame+7>: push %rbx 0x00000000009af3b5 <start_frame+8>: sub $0x10,%rsp 226 H264Context * const h = avctx->priv_data; 0x00000000009af3b9 <start_frame+12>: mov 0x98(%rdi),%rbx 227 MpegEncContext * const s = &h->s; 228 struct vaapi_context * const vactx = avctx->hwaccel_context; 0x00000000009af3c0 <start_frame+19>: mov 0x3e8(%rdi),%r12 229 VAPictureParameterBufferH264 *pic_param; 230 VAIQMatrixBufferH264 *iq_matrix; 231 232 av_dlog(avctx, "start_frame()\n"); 233 234 vactx->slice_param_size = sizeof(VASliceParameterBufferH264); => 0x00000000009af3c7 <start_frame+26>: movl $0x828,0x38(%r12) 235 236 /* Fill in VAPictureParameterBufferH264. */ 237 pic_param = ff_vaapi_alloc_pic_param(vactx, sizeof(VAPictureParameterBufferH264)); 0x00000000009af3d0 <start_frame+35>: mov $0x170,%esi 0x00000000009af3d5 <start_frame+40>: mov %r12,%rdi 0x00000000009af3d8 <start_frame+43>: callq 0xa9f079 <ff_vaapi_alloc_pic_param> 0x00000000009af3dd <start_frame+48>: mov %rax,%rbp 238 if (!pic_param) 0x00000000009af3e0 <start_frame+51>: test %rax,%rax ---Type <return> to continue, or q <return> to quit---q Quit (gdb) info locals h = 0x2504250 s = 0x2504250 vactx = 0x0 pic_param = <optimized out> iq_matrix = <optimized out> (gdb) info registers rax 0x10995a0 17405344 rbx 0x2504250 38814288 rcx 0x0 0 rdx 0x0 0 rsi 0x0 0 rdi 0x1b098c0 28350656 rbp 0x2504250 0x2504250 rsp 0x7fffe13b5c90 0x7fffe13b5c90 r8 0x1 1 r9 0x0 0 r10 0x0 0 r11 0x2 2 r12 0x0 0 r13 0x0 0 r14 0x0 0 r15 0x415f 16735 rip 0x9af3c7 0x9af3c7 <start_frame+26> eflags 0x10206 [ PF IF RF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0 }}} -- Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/824> FFmpeg <http://ffmpeg.org> FFmpeg issue tracker