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[Bug 463301] New: Race condition in the glibc function vfprintf()
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Fri, 2 Jan 2009 10:47:08 -0700 (MST)
  • Message-id: <bug-463301-21960@xxxxxxxxxxxxxxxxxxxxxxxxx/>

Summary: Race condition in the glibc function vfprintf()
Product: openSUSE 11.1
Version: Final
Platform: x86-64
OS/Version: openSUSE 11.1
Status: NEW
Severity: Normal
Priority: P5 - None
Component: Basesystem
AssignedTo: bnc-team-screening@xxxxxxxxxxxxxxxxxxxxxx
ReportedBy: bart.vanassche@xxxxxxxxx
QAContact: qa@xxxxxxx
Found By: Community User

Apparently calling printf() from more than one thread triggers a race condition
on _IO_2_1_stdout_.file._mode. This race is triggered by line 1270 of file
vfprintf.c, which contains the following statement: "ORIENT;". This statement
tests some bits in _IO_2_1_stdout_.file._mode and takes a decision. Later on
vfprintf() calls _IO_flockfile(). This is a race condition because other
threads may change these bits after vfprintf() tested these bits and before
vfprintf() calls _IO_flockfile().

I discovered this issue through verifying a multithreaded program with DRD (a
data race detection tool). The first error message printed by DRD for a program
that calls printf() from more than one thread is as follows:

$ svn info .
URL: svn://
Revision: 8895
$ ./vg-in-place --var-info=yes --tool=drd drd/tests/circular_buffer
==9097== Thread 3:
==9097== Conflicting load by thread 3/3 at 0x0539d840 size 4
==9097== at 0x508D460: vfprintf (vfprintf.c:1270)
==9097== by 0x5097599: printf (printf.c:35)
==9097== by 0x400D99: buffer_send (circular_buffer.c:105)
==9097== by 0x400E08: producer (circular_buffer.c:124)
==9097== by 0x4C2A047: vg_thread_wrapper (drd_pthread_intercepts.c:184)
==9097== by 0x4E3506F: start_thread (pthread_create.c:297)
==9097== by 0x511D0EC: clone (clone.S:112)
==9097== Location 0x539d840 is 0 bytes inside _IO_2_1_stdout_.file._mode,
==9097== a global variable declared at stdfiles.c:70

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