[Bug 838975] Re: weird pthread/fork race/deadlock

[Launchpad Bug Tracker]

This bug was fixed in the package eglibc - 2.13-20ubuntu3

---------------
eglibc (2.13-20ubuntu3) oneiric; urgency=low

  * Fix pthread/fork race/deadlock. LP: #838975.
    - Avoid race between {,__de}allocate_stack and __reclaim_stacks during fork.

  * Merge from Debian:

  [ Aurelien Jarno ]
  * Add debian/patches/cvs-dl_close-scope-handling.diff from upstream to
    fix issues with dl_close() when resolving locally-defined symbols.
    Closes: #625250.
  * patches/i386/local-cpuid-level2.diff: fix a typo.  Closes: #609389.
 -- Matthias Klose <doko at ubuntu.com>   Mon, 26 Sep 2011 13:50:14 +0200

** Changed in: eglibc (Ubuntu Oneiric)
       Status: Triaged => Fix Released

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https://bugs.launchpad.net/bugs/838975

Title:
  weird pthread/fork race/deadlock

Status in “eglibc” package in Ubuntu:
  Fix Released
Status in “eglibc” source package in Oneiric:
  Fix Released
Status in “glibc” package in Fedora:
  Unknown

Bug description:
  There appears to be a strange bug in glibc that causes deadlocks when
  calling fork() from threads.  We had a testcase in GLib failing from
  time to time because of this.

  I've attached a minimal testcase that uses only pure pthreads + libc.
  Compile it with -pthread and run it.  It should fill your screen with
  dots for a while, then hang when it hits the bug (which happens
  randomly anywhere between 1 dot and hundreds).  I've already received
  independent verification that this testcase hangs on several people's
  computers.

  I believe this to be an upstream issue since this bug is visible on
  Fedora 15 and 16, but the glibc website says I should file bugs
  against distributions first.  I also believe the issue to be a
  regression since Lucid is fine but Oneiric is not.  The problem
  appears to affect both 32 and 64bits.

  Some notes:

   - compiling the testcase with -static has the side-effect of causing
  the bug to go away

   - compiling the testcase with -DFORK_DIRECTLY also appears to solve
  the problem

   - replacing the execv() with a direct exit(0) doesn't solve the
  problem but causes the frequency to change

  
  The fact that both static linking and making the fork() syscall directly cause the problem to disappear leads me to believe that this is a libc bug rather than a kernel bug (which is the only other possibility).  I'm not 100% sure of that, though, since libc actually uses the clone() syscall to implement fork(), so there could be a different inside the kernel because of that.

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