[Bug 841634] Re: libc6 pthread_cond_wait fails to reacquire mutex upon cancellation

[Rémi Denis-Courmont]

** Attachment added: "Test case"
   https://bugs.launchpad.net/bugs/841634/+attachment/2356240/+files/condfail.c

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https://bugs.launchpad.net/bugs/841634

Title:
  libc6 pthread_cond_wait fails to reacquire mutex upon cancellation

Status in “eglibc” package in Ubuntu:
  New

Bug description:
  pthread_cond_wait() fails to re-acquire the provided mutex when acting
  on a deferred cancellation event from another thread. I initially hit
  the bug from the VLC media player test suite, but I wrote a simple
  reduced test case (attached).

  # gcc -O2 -Wall condfail.c -lpthread -o condfail
  # ./condfail
  1
  2
  a.out: condfail.c:18: cleanup_lock: Assertion `val == 0' failed.
  Aborted

  This is a violation of POSIX threads semantics. This also renders VLC
  media player debug versions completely unusable on affected systems.
  As a side note, this bug looks awfully similar to old Debian bug
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=551903

  Running stock Ubuntu 2.6.38-11-generic kernel and libc6 2.13-0ubuntu13. If this is any use, CPU information follows:
  % cat /proc/cpuinfo 
  processor       : 0
  vendor_id       : GenuineIntel
  cpu family      : 6
  model           : 14
  model name      : Genuine Intel(R) CPU           T2400  @ 1.83GHz
  stepping        : 8
  cpu MHz         : 1000.000
  cache size      : 2048 KB
  physical id     : 0
  siblings        : 2
  core id         : 0
  cpu cores       : 2
  apicid          : 0
  initial apicid  : 0
  fdiv_bug        : no
  hlt_bug         : no
  f00f_bug        : no
  coma_bug        : no
  fpu             : yes
  fpu_exception   : yes
  cpuid level     : 10
  wp              : yes
  flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc arch_perfmon bts aperfmperf pni monitor vmx est tm2 xtpr pdcm dts
  bogomips        : 3657.21
  clflush size    : 64
  cache_alignment : 64
  address sizes   : 32 bits physical, 32 bits virtual
  power management:

  processor       : 1
  vendor_id       : GenuineIntel
  cpu family      : 6
  model           : 14
  model name      : Genuine Intel(R) CPU           T2400  @ 1.83GHz
  stepping        : 8
  cpu MHz         : 1000.000
  cache size      : 2048 KB
  physical id     : 0
  siblings        : 2
  core id         : 1
  cpu cores       : 2
  apicid          : 1
  initial apicid  : 1
  fdiv_bug        : no
  hlt_bug         : no
  f00f_bug        : no
  coma_bug        : no
  fpu             : yes
  fpu_exception   : yes
  cpuid level     : 10
  wp              : yes
  flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc arch_perfmon bts aperfmperf pni monitor vmx est tm2 xtpr pdcm dts
  bogomips        : 3657.55
  clflush size    : 64
  cache_alignment : 64
  address sizes   : 32 bits physical, 32 bits virtual
  power management:

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