Commit 60f2ceaa authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Thomas Gleixner
Browse files

posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group 



As of e78c3496 ("time, signal: Protect resource use statistics
with seqlock") cpu_clock_sample_group no longers needs siglock
protection.  Unfortunately no one realized it at the time.

Remove the extra locking that is for cpu_clock_sample_group and not
for cpu_clock_sample.  This significantly simplifies the code.

Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/878skmvdts.fsf@x220.int.ebiederm.org
parent a2efdbf4

kernel/time/posix-cpu-timers.c

+12 −54
Original line number Diff line number Diff line
@@ -718,31 +718,10 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp 
	/*

	 * Sample the clock to take the difference with the expiry time.

	 */

	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {

	if (CPUCLOCK_PERTHREAD(timer->it_clock))

		now = cpu_clock_sample(clkid, p);

	} else {

		struct sighand_struct *sighand;

		unsigned long flags;



		/*

		 * Protect against sighand release/switch in exit/exec and

		 * also make timer sampling safe if it ends up calling

		 * thread_group_cputime().

		 */

		sighand = lock_task_sighand(p, &flags);

		if (unlikely(sighand == NULL)) {

			/*

			 * The process has been reaped.

			 * We can't even collect a sample any more.

			 * Disarm the timer, nothing else to do.

			 */

			cpu_timer_setexpires(ctmr, 0);

			return;

		} else {

	else

		now = cpu_clock_sample_group(clkid, p, false);

			unlock_task_sighand(p, &flags);

		}

	}



	if (now < expires) {

		itp->it_value = ns_to_timespec64(expires - now);
@@ -986,43 +965,22 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer) 
	/*

	 * Fetch the current sample and update the timer's expiry time.

	 */

	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {

	if (CPUCLOCK_PERTHREAD(timer->it_clock))

		now = cpu_clock_sample(clkid, p);

	else

		now = cpu_clock_sample_group(clkid, p, true);



	bump_cpu_timer(timer, now);

		if (unlikely(p->exit_state))

			return;



	/* Protect timer list r/w in arm_timer() */

	sighand = lock_task_sighand(p, &flags);

		if (!sighand)

			return;

	} else {

		/*

		 * Protect arm_timer() and timer sampling in case of call to

		 * thread_group_cputime().

		 */

		sighand = lock_task_sighand(p, &flags);

		if (unlikely(sighand == NULL)) {

			/*

			 * The process has been reaped.

			 * We can't even collect a sample any more.

			 */

			cpu_timer_setexpires(ctmr, 0);

	if (unlikely(sighand == NULL))

		return;

		} else if (unlikely(p->exit_state) && thread_group_empty(p)) {

			/* If the process is dying, no need to rearm */

			goto unlock;

		}

		now = cpu_clock_sample_group(clkid, p, true);

		bump_cpu_timer(timer, now);

		/* Leave the sighand locked for the call below.  */

	}



	/*

	 * Now re-arm for the new expiry time.

	 */

	arm_timer(timer);

unlock:

	unlock_task_sighand(p, &flags);

}

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