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Commit 1f169f84 authored by Stanislaw Gruszka's avatar Stanislaw Gruszka Committed by Thomas Gleixner
Browse files

cpu-timers: Change SIGEV_NONE timer implementation 



When user sets up a timer without associated signal and process does
not use any other cpu timers and does not exit, tsk->signal->cputimer
is enabled and running forever.

Avoid running the timer for no reason.

I used below program to check patch does not break current user space
visible behavior.

 #include <sys/time.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
 #include <assert.h>

 void consume_cpu(void)
 {
	int i = 0;
	int count = 0;

	for(i=0; i<100000000; i++)
		count++;
 }

 int main(void)
 {
	int i;
	struct sigaction act;
	struct sigevent evt = { };
	timer_t tid;
	struct itimerspec spec = { };

	evt.sigev_notify = SIGEV_NONE;
	assert(timer_create(CLOCK_PROCESS_CPUTIME_ID, &evt,  &tid) == 0);

	spec.it_value.tv_sec = 10;
	assert(timer_settime(tid, 0, &spec,  NULL) == 0);

	for (i = 0; i < 30; i++) {
		consume_cpu();
		memset(&spec, 0, sizeof(spec));
		assert(timer_gettime(tid, &spec) == 0);
		printf("%lu.%09lu\n",
			(unsigned long) spec.it_value.tv_sec,
			(unsigned long) spec.it_value.tv_nsec);
	}

	assert(timer_delete(tid) == 0);
	return 0;
 }

Signed-off-by: default avatarStanislaw Gruszka <sgruszka@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent ae1a78ee

kernel/posix-cpu-timers.c

+6 −22
Original line number Original line Diff line number Diff line
@@ -615,7 +615,12 @@ static void arm_timer(struct k_itimer *timer) 
 */

 */

static void cpu_timer_fire(struct k_itimer *timer)

static void cpu_timer_fire(struct k_itimer *timer)

{

{

	if (unlikely(timer->sigq == NULL)) {

	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {

		/*

		 * User don't want any signal.

		 */

		timer->it.cpu.expires.sched = 0;

	} else if (unlikely(timer->sigq == NULL)) {

		/*

		/*

		 * This a special case for clock_nanosleep,

		 * This a special case for clock_nanosleep,

		 * not a normal timer from sys_timer_create.

		 * not a normal timer from sys_timer_create.
@@ -784,7 +789,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, 
	 */

	 */

	timer->it.cpu.expires = new_expires;

	timer->it.cpu.expires = new_expires;

	if (new_expires.sched != 0 &&

	if (new_expires.sched != 0 &&

	    (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&

	    cpu_time_before(timer->it_clock, val, new_expires)) {

	    cpu_time_before(timer->it_clock, val, new_expires)) {

		arm_timer(timer);

		arm_timer(timer);

	}

	}
@@ -809,7 +813,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, 
	timer->it_overrun = -1;

	timer->it_overrun = -1;





	if (new_expires.sched != 0 &&

	if (new_expires.sched != 0 &&

	    (timer->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE &&

	    !cpu_time_before(timer->it_clock, val, new_expires)) {

	    !cpu_time_before(timer->it_clock, val, new_expires)) {

		/*

		/*

		 * The designated time already passed, so we notify

		 * The designated time already passed, so we notify
@@ -883,25 +886,6 @@ void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp) 
		read_unlock(&tasklist_lock);

		read_unlock(&tasklist_lock);

	}

	}





	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {

		if (timer->it.cpu.incr.sched == 0 &&

		    cpu_time_before(timer->it_clock,

				    timer->it.cpu.expires, now)) {

			/*

			 * Do-nothing timer expired and has no reload,

			 * so it's as if it was never set.

			 */

			timer->it.cpu.expires.sched = 0;

			itp->it_value.tv_sec = itp->it_value.tv_nsec = 0;

			return;

		}

		/*

		 * Account for any expirations and reloads that should

		 * have happened.

		 */

		bump_cpu_timer(timer, now);

	}



	if (unlikely(clear_dead)) {

	if (unlikely(clear_dead)) {

		/*

		/*

		 * We've noticed that the thread is dead, but

		 * We've noticed that the thread is dead, but