Commit ee3ece83 authored Jul 03, 2008 by Steven Rostedt Committed by Linus Torvalds Jul 03, 2008

hrtimer: prevent migration for raising softirq



Due to a possible deadlock, the waking of the softirq was pushed outside
of the hrtimer base locks. See commit 0c96c597

Unfortunately this allows the task to migrate after setting up the softirq
and raising it. Since softirqs run a queue that is per-cpu we may raise the
softirq on the wrong CPU and this will keep the queued softirq task from
running.

To solve this issue, this patch disables preemption around the releasing
of the hrtimer lock and raising of the softirq.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6beef7eb

kernel/hrtimer.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -1003,10 +1003,18 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
		*/
		raise = timer->state == HRTIMER_STATE_PENDING;

		/*
		* We use preempt_disable to prevent this task from migrating after
		* setting up the softirq and raising it. Otherwise, if me migrate
		* we will raise the softirq on the wrong CPU.
		*/
		preempt_disable();

		unlock_hrtimer_base(timer, &flags);

		if (raise)
		hrtimer_raise_softirq();
		preempt_enable();

		return ret;
		}

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