>Number: 162403
>Category: misc
>Synopsis: regression in FreeBSD/9 regarding pthread timeouts in kernel
>context
>Confidential: no
>Severity: serious
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Nov 09 14:10:09 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator: Armin Gruner
>Release: FreeBSD 9.0-RC1
>Organization:
muc.de
>Environment:
FreeBSD ag.techsat.com 9.0-RC1 FreeBSD 9.0-RC1 #1 r226966M: Mon Oct 31 15:11:15
CET 2011 [email protected]:/usr/obj/usr/src/sys/GENERIC i386
>Description:
pthread operations with a given timeout don't work under FreeBSD 9,
if the process is running in realtime priority context. The timeout
is not honoured at all.
>How-To-Repeat:
Compile the given code snippet with cc -pthread.
It has two threads, one waiting for a condition to fire up.
The producer delays initial signaling of the condition when started;
thus the consumer should timeout after five seconds.
Afterwards, it will be signaled every three seconds.
The call to pthread_cond_timedwait() properly times out if the process is not
running with RT prio:
[ag@ag 1024]$ uname -a
FreeBSD ag.techsat.com 9.0-RC1 FreeBSD 9.0-RC1 #1 r226966M: Mon Oct
31 15:11:15 CET 2011 ag@ag:/usr/obj/usr/src/sys/GENERIC i386
[ag@ag 1017]$ ./tt
tt: pthread_cond_timedwait: Operation timed out
WOKE UP
WOKE UP
It does not honour the timeout if running with realtime priority:
[ag@ag 1020]$ SU rtprio 31 ./tt
~/work/c
WOKE UP
WOKE UP
Under FreeBSD/8, both user and kernel pthread contexts works as expected:
$ uname -a
FreeBSD release-pc-freebsd 8.2-RELEASE FreeBSD 8.2-RELEASE #0: Fri Feb 18
02:24:46 UTC 2011 [email protected]:/usr/obj/usr/src/sys/GENERIC
i386
$ ./tt
tt: pthread_cond_timedwait: Operation timed out
WOKE UP
WOKE UP
[ag@release-pc-freebsd 369]$ SU rtprio 31 ./tt
tt: pthread_cond_timedwait: Operation timed out
WOKE UP
WOKE UP
>Fix:
Patch attached with submission follows:
#include <stdio.h>
#include <time.h>
#include <pthread.h>
pthread_mutex_t mtx;
pthread_cond_t cnd;
void *
loop(void *dummy)
{
int rc;
struct timespec abstime;
while (1)
{
clock_gettime(CLOCK_REALTIME, &abstime);
abstime.tv_sec += 5;
rc = pthread_mutex_lock(&mtx);
if (rc != 0)
warnc(rc, "pthread_mutex_lock");
rc = pthread_cond_timedwait(&cnd, &mtx, &abstime);
if (rc != 0)
warnc(rc, "pthread_cond_timedwait");
else
fprintf(stderr, "WOKE UP\n");
rc = pthread_mutex_unlock(&mtx);
if (rc != 0)
warnc(rc, "pthread_mutex_unlock");
}
return NULL;
}
main()
{
int rc;
pthread_t t1;
struct sched_param sp;
rc = pthread_mutex_init(&mtx, NULL);
if (rc != 0)
warnc(rc, "pthread_mutex_init");
rc = pthread_cond_init(&cnd, NULL);
if (rc != 0)
warnc(rc, "pthread_cond_init");
pthread_create(&t1, NULL, loop, NULL);
sleep(8);
while (1)
{
rc = pthread_mutex_lock(&mtx);
if (rc != 0)
warnc(rc, "pthread_mutex_lock");
rc = pthread_cond_signal(&cnd);
if (rc != 0)
warnc(rc, "pthread_cond_signal");
rc = pthread_mutex_unlock(&mtx);
if (rc != 0)
warnc(rc, "pthread_mutex_unlock");
sleep(3);
}
}
>Release-Note:
>Audit-Trail:
>Unformatted:
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