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[Bug nptl/14532] New: Generic sem_post race
- From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Thu, 30 Aug 2012 19:13:59 +0000
- Subject: [Bug nptl/14532] New: Generic sem_post race
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=14532
Bug #: 14532
Summary: Generic sem_post race
Product: glibc
Version: 2.16
Status: NEW
Severity: normal
Priority: P2
Component: nptl
AssignedTo: unassigned@sourceware.org
ReportedBy: jsm28@gcc.gnu.org
CC: drepper.fsp@gmail.com
Classification: Unclassified
The generic Linux version of sem_post (nptl/sysdeps/unix/sysv/linux/sem_post.c)
uses atomic_compare_and_exchange_bool_acq to increment the semaphore. This is
an unlock operation and should actually be using a release barrier. The
following test fails on some MIPS systems (MIPS uses the generic version of
sem_post where various architectures use their own .S versions). Testing a
patch.
#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#define NTHREADS 10
#define NITER 100000
sem_t sem;
int c;
volatile int thread_fail;
static void *
tf (void *arg)
{
for (int i = 0; i < NITER; i++)
{
if (sem_wait (&sem) != 0)
{
perror ("sem_wait");
thread_fail = 1;
}
++c;
if (sem_post (&sem) != 0)
{
perror ("sem_post");
thread_fail = 1;
}
}
return NULL;
}
int
main (void)
{
if (sem_init (&sem, 0, 0) != 0)
{
perror ("sem_init");
return 1;
}
pthread_t th[NTHREADS];
for (int i = 0; i < NTHREADS; i++)
{
if (pthread_create (&th[i], NULL, tf, NULL) != 0)
{
puts ("pthread_create failed");
return 1;
}
}
if (sem_post (&sem) != 0)
{
perror ("sem_post");
return 1;
}
for (int i = 0; i < NTHREADS; i++)
if (pthread_join (th[i], NULL) != 0)
{
puts ("pthread_join failed");
return 1;
}
if (c != NTHREADS * NITER)
{
printf ("c = %d, should be %d\n", c, NTHREADS * NITER);
return 1;
}
return thread_fail;
}
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