Bug 738665 - strange pthread/fork deadlock
Summary: strange pthread/fork deadlock
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: glibc
Version: 6.0
Hardware: All
OS: Linux
Target Milestone: rc
: ---
Assignee: Andreas Schwab
QA Contact: qe-baseos-tools-bugs
Depends On:
Blocks: 743047
TreeView+ depends on / blocked
Reported: 2011-09-15 13:49 UTC by Andreas Schwab
Modified: 2017-02-09 11:19 UTC (History)
3 users (show)

Fixed In Version: glibc-2.12-1.42.el6
Doc Type: Bug Fix
Doc Text:
Clone Of: 737387
: 759341 (view as bug list)
Last Closed: 2011-12-06 17:48:13 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2011:1526 0 normal SHIPPED_LIVE Low: glibc security, bug fix, and enhancement update 2011-12-06 01:02:21 UTC
Sourceware 13699 0 None None None 2017-02-09 11:19:24 UTC

Description Andreas Schwab 2011-09-15 13:49:16 UTC
+++ This bug was initially created as a clone of Bug #737387 +++

Created attachment 522617 [details]
test case demonstrating the issue

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 Ubuntu as well, but the glibc website says I should file bugs against distributions first. I also believe the issue to be a regression since older Fedora and RHEL releases are unaffected.  The problem appears to affect both 32 and 64bits.
Description of problem:

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

 - 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.

Comment 4 Shane Carr 2011-12-02 02:25:13 UTC
We are hitting this bug regularly in RHEL5 (glibc 2.5).  I have confirmed that the attached test case hangs on multiple machines.

Is there any chance of having the fix integrated into RHEL5?

Comment 5 errata-xmlrpc 2011-12-06 17:48:13 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.


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