[PATCH 2.6] fix POSIX timers expire before their scheduled time

[PATCH 2.6] fix POSIX timers expire before their scheduled time

[Liu, Hong]

POSIX says: POSIX timers should not expire before their scheduled time.

Due to the timer started between jiffies, there are cases that the timer
will expire before its scheduled time.
This patch ensures timers will not expire early.

--- a/kernel/posix-timers.c     2005-03-10 15:46:27.329333664 +0800
+++ b/kernel/posix-timers.c     2005-03-10 15:50:11.884196136 +0800
@@ -957,7 +957,8 @@
                            &expire_64, &(timr->wall_to_prev))) {
                return -EINVAL;
        }
-       timr->it_timer.expires = (unsigned long)expire_64;
+       timr->it_timer.expires = (unsigned long)expire_64 + 1;
        tstojiffie(&new_setting->it_interval, clock->res, &expire_64);
        timr->it_incr = (unsigned long)expire_64;

Re: [PATCH 2.6] fix POSIX timers expire before their scheduled time

[George Anzinger]

Liu, Hong wrote:
> POSIX says: POSIX timers should not expire before their scheduled time.
> 
> Due to the timer started between jiffies, there are cases that the timer
> will expire before its scheduled time.
> This patch ensures timers will not expire early.
> 
> --- a/kernel/posix-timers.c     2005-03-10 15:46:27.329333664 +0800
> +++ b/kernel/posix-timers.c     2005-03-10 15:50:11.884196136 +0800
> @@ -957,7 +957,8 @@
>                             &expire_64, &(timr->wall_to_prev))) {
>                 return -EINVAL;
>         }
> -       timr->it_timer.expires = (unsigned long)expire_64;
> +       timr->it_timer.expires = (unsigned long)expire_64 + 1;
>         tstojiffie(&new_setting->it_interval, clock->res, &expire_64);
>         timr->it_incr = (unsigned long)expire_64;
> 
Has this happened??  The following code (in adjust_abs_time()) is supposed to 
prevent this sort of thing:

	if (oc.tv_sec | oc.tv_nsec) {
		oc.tv_nsec += clock->res;
		timespec_norm(&oc);
	}

Also, we run rather extensive tests for this sort of thing.


-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/

Re: [PATCH 2.6] fix POSIX timers expire before their scheduled time

[Hong Liu]

[-- Attachment #1: Type: text/plain, Size: 1420 bytes --]

On Thu, 2005-03-17 at 14:29, George Anzinger wrote:
> Liu, Hong wrote:
> > POSIX says: POSIX timers should not expire before their scheduled time.
> > 
> > Due to the timer started between jiffies, there are cases that the timer
> > will expire before its scheduled time.
> > This patch ensures timers will not expire early.
> > 
> > --- a/kernel/posix-timers.c     2005-03-10 15:46:27.329333664 +0800
> > +++ b/kernel/posix-timers.c     2005-03-10 15:50:11.884196136 +0800
> > @@ -957,7 +957,8 @@
> >                             &expire_64, &(timr->wall_to_prev))) {
> >                 return -EINVAL;
> >         }
> > -       timr->it_timer.expires = (unsigned long)expire_64;
> > +       timr->it_timer.expires = (unsigned long)expire_64 + 1;
> >         tstojiffie(&new_setting->it_interval, clock->res, &expire_64);
> >         timr->it_incr = (unsigned long)expire_64;
> > 
> Has this happened??  The following code (in adjust_abs_time()) is supposed to 
> prevent this sort of thing:
> 
> 	if (oc.tv_sec | oc.tv_nsec) {
> 		oc.tv_nsec += clock->res;
> 		timespec_norm(&oc);
> 	}
> 
> Also, we run rather extensive tests for this sort of thing.
> 
The attached case from PosixTestSuite(http://posixtest.sourceforge.net)
failed on IA64 platform.
And if I changed the time interval to N*clock_res in this case, it will
also fail on IA32 platform.


BTW, I can't find the code piece you mentioned in 2.6.11 kernel.

[-- Attachment #2: 9-1.c --]
[-- Type: text/x-csrc, Size: 3695 bytes --]

/*   
 * Copyright (c) 2002, Intel Corporation. All rights reserved.
 * Created by:  julie.n.fleischer REMOVE-THIS AT intel DOT com
 * This file is licensed under the GPL license.  For the full content
 * of this license, see the COPYING file at the top level of this 
 * source tree.
 *
 * Test that timers are not allowed to expire before their scheduled
 * time.
 *
 * Test for a variety of timer values on relative timers.
 *
 * For this test, signal SIGTOTEST will be used, clock CLOCK_REALTIME
 * will be used.
 */

#include <time.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#define PTS_PASS        0
#define PTS_FAIL        1
#define PTS_UNRESOLVED  2
#define PTS_UNSUPPORTED 4
#define PTS_UNTESTED    5

#define SIGTOTEST SIGALRM
#define TIMERVALUESEC 2
#define TIMERINTERVALSEC 5
#define INCREMENT 1
#define ACCEPTABLEDELTA 1

#define NUMTESTS 6

static int timeroffsets[NUMTESTS][2] = { {0, 30000000}, {1, 0}, 
					{1, 30000000}, {2, 0},
					{1, 5000}, {1, 5} };

int main(int argc, char *argv[])
{
	struct sigevent ev;
	timer_t tid;
	struct itimerspec its;
	struct timespec tsbefore, tsafter;
	sigset_t set;
	int sig;
	int i;
	int failure = 0;
	unsigned long totalnsecs, testnsecs; // so long was we are < 2.1 seconds, we should be safe

	/*
	 * set up signal set containing SIGTOTEST that will be used
	 * in call to sigwait immediately after timer is set
	 */

	if (sigemptyset(&set) == -1 ) {
		perror("sigemptyset() failed\n");
		return PTS_UNRESOLVED;
	}

	if (sigaddset(&set, SIGTOTEST) == -1) {
		perror("sigaddset() failed\n");
		return PTS_UNRESOLVED;
	}

        if (sigprocmask (SIG_BLOCK, &set, NULL) == -1) {
                perror("sigprocmask() failed\n");
                return PTS_UNRESOLVED;
        }

	/*
	 * set up timer to perform action SIGTOTEST on expiration
	 */
	ev.sigev_notify = SIGEV_SIGNAL;
	ev.sigev_signo = SIGTOTEST;

	if (timer_create(CLOCK_REALTIME, &ev, &tid) != 0) {
		perror("timer_create() did not return success\n");
		return PTS_UNRESOLVED;
	}

	for (i = 0; i < NUMTESTS; i++) {
		its.it_interval.tv_sec = 0; its.it_interval.tv_nsec = 0;
		its.it_value.tv_sec = timeroffsets[i][0];
		its.it_value.tv_nsec = timeroffsets[i][1];

		printf("Test for value %d sec %d nsec\n", 
				(int) its.it_value.tv_sec,
				(int) its.it_value.tv_nsec);

		if (clock_gettime(CLOCK_REALTIME, &tsbefore) != 0) {
			perror("clock_gettime() did not return success\n");
			return PTS_UNRESOLVED;
		}
		
		if (timer_settime(tid, 0, &its, NULL) != 0) {
			perror("timer_settime() did not return success\n");
			return PTS_UNRESOLVED;
		}
	
		if (sigwait(&set, &sig) == -1) {
			perror("sigwait() failed\n");
			return PTS_UNRESOLVED;
		}
	
		if (clock_gettime(CLOCK_REALTIME, &tsafter) != 0) {
			perror("clock_gettime() did not return success\n");
			return PTS_UNRESOLVED;
		}
	
		
		printf("tsbefore: sec--%lu, nsec--%lu\n", tsbefore.tv_sec,
							tsbefore.tv_nsec);
		printf("tsafter:  sec--%lu, nsec--%lu\n", tsafter.tv_sec,
							tsafter.tv_nsec);
		totalnsecs = (unsigned long) (tsafter.tv_sec-tsbefore.tv_sec)*
					1000000000 +
					(tsafter.tv_nsec-tsbefore.tv_nsec);
		testnsecs = (unsigned long) its.it_value.tv_sec*1000000000 + 
					its.it_value.tv_nsec;
		printf("total %lu test %lu\n", totalnsecs, testnsecs);
		if (totalnsecs < testnsecs) {
			printf("FAIL:  Expired %ld < %ld\n", totalnsecs,
							testnsecs);
			failure = 1;
		}
	}

	if (timer_delete(tid) != 0) {
		perror("timer_delete() did not return success\n");
		return PTS_UNRESOLVED;
	}

	if (failure) {
		printf("timer_settime() failed on at least one value\n");
		return PTS_FAIL;
	} else {
		printf("Test PASSED\n");
		return PTS_PASS;
	}
}