Bug 738665

Summary:	strange pthread/fork deadlock
Product:	Red Hat Enterprise Linux 6	Reporter:	Andreas Schwab <schwab>
Component:	glibc	Assignee:	Andreas Schwab <schwab>
Status:	CLOSED ERRATA	QA Contact:	qe-baseos-tools-bugs
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	6.0	CC:	fweimer, mfranc, scarr6
Target Milestone:	rc
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	glibc-2.12-1.42.el6	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:	737387
Clones:	759341 (view as bug list)		Environment:
Last Closed:	2011-12-06 17:48:13 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	743047

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
   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.

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.

http://rhn.redhat.com/errata/RHSA-2011-1526.html