[FFmpeg-cvslog] avcodec/ff_init_vlc_sparse: use a spinlock for thread sync

[Carl Eugen Hoyos]

Michael Niedermayer <git <at> videolan.org> writes:

> ffmpeg | branch: master | Michael Niedermayer | 
> Sat Jul 13 13:32:39 2013 +0200|
> [6af8326354ed6c1c68b53b3f2bba6697fb2d3bff] | 
> committer: Michael Niedermayer
> 
> avcodec/ff_init_vlc_sparse: use a spinlock for thread sync

This commit leads to many deadlocks when running fate 
on AIX PPC64, for example when reading the mp2 file 
produced by fate-acodec-mp2.
The deadlock is not reproducible if I disable all decoders 
except mp2, it is reproducible (for example) if I enable
the mp2 and the mpeg2video decoder.

Carl Eugen

(gdb) r -i tests/data/fate/acodec-mp2.mp2
Starting program: ffmpeg_g -i tests/data/fate/acodec-mp2.mp2
[New Thread 1]
ffmpeg version N-63983-gbc21260 Copyright (c) 2000-2014 the FFmpeg developers
  built on Jun 15 2014 15:34:47 with gcc 4.8.1 (GCC)
  configuration: --enable-debug=3 --cc='gcc -maix64' 
--disable-encoders --enable-encoder=mp2
  libavutil      52. 89.100 / 52. 89.100
  libavcodec     55. 66.101 / 55. 66.101
  libavformat    55. 43.100 / 55. 43.100
  libavdevice    55. 13.101 / 55. 13.101
  libavfilter     4.  8.100 /  4.  8.100
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 19.100 /  0. 19.100

Program received signal SIGINT, Interrupt.
[Switching to Thread 1]
0x00000001002e798c in ff_init_vlc_sparse (vlc=0x11051e5bc
<_mpegaudiodecfixed.bss_+255416>,
    nb_bits=7, nb_codes=512, bits=0xfffffffffffe570, bits_wrap=1, bits_size=1,
    codes=0xfffffffffffe170, codes_wrap=2, codes_size=2, symbols=0x0,
symbols_wrap=0,
    symbols_size=0, flags=4) at ./libavutil/atomic_gcc.h:57
57          return __sync_val_compare_and_swap(ptr, oldval, newval);
(gdb) bt
#0  0x00000001002e798c in ff_init_vlc_sparse (
    vlc=0x11051e5bc <_mpegaudiodecfixed.bss_+255416>, nb_bits=7, nb_codes=512,
    bits=0xfffffffffffe570, bits_wrap=1, bits_size=1,
codes=0xfffffffffffe170, codes_wrap=2,
    codes_size=2, symbols=0x0, symbols_wrap=0, symbols_size=0, flags=4)
    at ./libavutil/atomic_gcc.h:57
#1  0x00000001006cdc94 in decode_init_static () at  _start_ :311
#2  0x00000001006ce2fc in decode_init (avctx=<error reading variable>) at 
_start_ :415
#3  0x0000000100022714 in avcodec_open2 (avctx=0x110655b40,
    codec=0x110046c50 <ff_mp3_decoder>, options=0x110655fc0) at
libavcodec/utils.c:1546
#4  0x00000001000f03a4 in avformat_find_stream_info (ic=0x110654f80,
options=0x110655fc0)
    at libavformat/utils.c:69
#5  0x00000001002cc064 in open_input_file (o=0xffffffffffff0e0,
    filename=0xffffffffffffc3a "out.mp2") at ffmpeg_opt.c:106
#6  0x00000001002d0fa4 in ffmpeg_parse_options (argc=-3872, argv=0x0) at
ffmpeg_opt.c:2645
#7  0x000000010000063c in main (argc=<error reading variable>, argv=<error
reading variable>)
    at  _start_ :3807
(gdb) disass $pc-32,$pc+32
Dump of assembler code from 0x1002e796c to 0x1002e79ac:
   0x00000001002e796c <ff_init_vlc_sparse+164>: beq     0x1002e79c8
<ff_init_vlc_sparse+256>
   0x00000001002e7970 <ff_init_vlc_sparse+168>: addi    r8,r3,24
   0x00000001002e7974 <ff_init_vlc_sparse+172>: addi    r6,r3,32
   0x00000001002e7978 <ff_init_vlc_sparse+176>: sync
   0x00000001002e797c <ff_init_vlc_sparse+180>: ldarx   r9,0,r8
   0x00000001002e7980 <ff_init_vlc_sparse+184>: cmpdi   cr7,r9,0
   0x00000001002e7984 <ff_init_vlc_sparse+188>: bne     cr7,0x1002e7990
<ff_init_vlc_sparse+200>
   0x00000001002e7988 <ff_init_vlc_sparse+192>: stdcx.  r25,0,r8
=> 0x00000001002e798c <ff_init_vlc_sparse+196>: bne     0x1002e797c
<ff_init_vlc_sparse+180>
   0x00000001002e7990 <ff_init_vlc_sparse+200>: isync
   0x00000001002e7994 <ff_init_vlc_sparse+204>: beq     cr7,0x1002e7a58
<ff_init_vlc_sparse+400>
   0x00000001002e7998 <ff_init_vlc_sparse+208>: cmpld   cr7,r9,r6
   0x00000001002e799c <ff_init_vlc_sparse+212>: bne     cr7,0x1002e7978
<ff_init_vlc_sparse+176>
   0x00000001002e79a0 <ff_init_vlc_sparse+216>: lwz     r9,16(r25)
   0x00000001002e79a4 <ff_init_vlc_sparse+220>: cmpwi   cr7,r9,0
   0x00000001002e79a8 <ff_init_vlc_sparse+224>: beq     cr7,0x1002e8028
<ff_init_vlc_sparse+1888>
End of assembler dump.
(gdb) info register
r0             0x4      4
r1             0xfffffffffffb0d0        1152921504606826704
r2             0x1100bc568      4564174184
r3             0x11051e5bc      4568769980
r4             0x7      7
r5             0x200    512
r6             0x11051e5dc      4568770012
r7             0x1      1
r8             0x11051e5d4      4568770004
r9             0x0      0
r10            0x2      2
r11            0x4      4
r12            0x44224242       1143095874
r13            0x110644d20      4569976096
r14            0x4      4
r15            0x0      0
r16            0x4      4
r17            0xfffffffffffe170        1152921504606839152
r18            0x1      1
r19            0xfffffffffffe570        1152921504606840176
r20            0x4      4
r21            0x0      0
r22            0x200    512
r23            0x2      2
r24            0x2      2
r25            0x11051e5bc      4568769980
r26            0x7      7
r27            0x0      0
r28            0x110046ea0      4563693216
r29            0x100a54fb0      4305801136
r30            0x44224242       1143095874
r31            0x0      0
pc             0x1002e798c      0x1002e798c <ff_init_vlc_sparse+196>
msr            0xa00000000200d032       11529215046102077490
cr             0x4224242        69354050
lr             0x1006cdc94      0x1006cdc94 <decode_init_static+680>
ctr            0x0      0
xer            0x2006c180       537313664