Attachment 310963 Details for Bug 452693 – hrtimer: prevent migration for raising CPU

[patch] hrtimer: prevent migration for raising CPU

hrtimer-dont-migrate-raisesoftirq.patch (text/plain), 1.24 KB, created by Clark Williams on 2008-07-03 20:54:22 UTC

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Creator: Clark Williams

Created: 2008-07-03 20:54:22 UTC

Size: 1.24 KB

patch

obsolete

>From: Steven Rostedt <srostedt@redhat.com>
>Subject: hrtimer: prevent migration for raising CPU
>
>Due to a possible deadlock, the waking of the softirq was pushed outside
>of the hrtimer base locks. 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>
>
>Index: linux-2.6.24.7.noarch/kernel/hrtimer.c
>===================================================================
>--- linux-2.6.24.7.noarch.orig/kernel/hrtimer.c
>+++ linux-2.6.24.7.noarch/kernel/hrtimer.c
>@@ -930,10 +930,18 @@ hrtimer_start(struct hrtimer *timer, kti
> 	 */
> 	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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Attachments on bug 452693: 310481 | 310594 | 310598 | 310963