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Commit c2873937 authored by Stanislaw Gruszka's avatar Stanislaw Gruszka Committed by Thomas Gleixner
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cpu-timers: Avoid iterating over all threads in fastpath_timer_check() 



Spread p->sighand->siglock locking scope to make sure that
fastpath_timer_check() never iterates over all threads. Without
locking there is small possibility that signal->cputimer will stop
running while we write values to signal->cputime_expires.

Calling thread_group_cputime() from fastpath_timer_check() is not only
bad because it is slow, also it is racy with __exit_signal() which can
lead to invalid signal->{s,u}time values.

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 1f169f84

kernel/posix-cpu-timers.c

+7 −7
Original line number Diff line number Diff line
@@ -550,7 +550,7 @@ static inline int expires_gt(cputime_t expires, cputime_t new_exp) 
/*

 * Insert the timer on the appropriate list before any timers that

 * expire later.  This must be called with the tasklist_lock held

 * for reading, and interrupts disabled.

 * for reading, interrupts disabled and p->sighand->siglock taken.

 */

static void arm_timer(struct k_itimer *timer)

{
@@ -569,9 +569,6 @@ static void arm_timer(struct k_itimer *timer) 
	}

	head += CPUCLOCK_WHICH(timer->it_clock);



	BUG_ON(!irqs_disabled());

	spin_lock(&p->sighand->siglock);



	listpos = head;

	list_for_each_entry(next, head, entry) {

		if (cpu_time_before(timer->it_clock, nt->expires, next->expires))
@@ -606,8 +603,6 @@ static void arm_timer(struct k_itimer *timer) 
			break;

		}

	}



	spin_unlock(&p->sighand->siglock);

}



/*
@@ -720,7 +715,6 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, 
		ret = TIMER_RETRY;

	} else

		list_del_init(&timer->it.cpu.entry);

	spin_unlock(&p->sighand->siglock);



	/*

	 * We need to sample the current value to convert the new
@@ -774,6 +768,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, 
		 * disable this firing since we are already reporting

		 * it as an overrun (thanks to bump_cpu_timer above).

		 */

		spin_unlock(&p->sighand->siglock);

		read_unlock(&tasklist_lock);

		goto out;

	}
@@ -793,6 +788,7 @@ int posix_cpu_timer_set(struct k_itimer *timer, int flags, 
		arm_timer(timer);

	}



	spin_unlock(&p->sighand->siglock);

	read_unlock(&tasklist_lock);



	/*
@@ -1206,6 +1202,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) 
			goto out;

		}

		read_lock(&tasklist_lock); /* arm_timer needs it.  */

		spin_lock(&p->sighand->siglock);

	} else {

		read_lock(&tasklist_lock);

		if (unlikely(p->signal == NULL)) {
@@ -1226,6 +1223,7 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) 
			clear_dead_task(timer, now);

			goto out_unlock;

		}

		spin_lock(&p->sighand->siglock);

		cpu_timer_sample_group(timer->it_clock, p, &now);

		bump_cpu_timer(timer, now);

		/* Leave the tasklist_lock locked for the call below.  */
@@ -1234,7 +1232,9 @@ void posix_cpu_timer_schedule(struct k_itimer *timer) 
	/*

	 * Now re-arm for the new expiry time.

	 */

	BUG_ON(!irqs_disabled());

	arm_timer(timer);

	spin_unlock(&p->sighand->siglock);



out_unlock:

	read_unlock(&tasklist_lock);