linux-kernel - Re: [PATCH] hrtimer: prevent migration for raising softirq

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Message-ID: <Pine.LNX.4.58.0807032148340.7798@gandalf.stny.rr.com>
Date:	Thu, 3 Jul 2008 21:56:00 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, akpm@...uxfoundation.org,
	peterz@...radead.org, stable@...nel.org
Subject: Re: [PATCH] hrtimer: prevent migration for raising softirq



On Thu, 3 Jul 2008, Andrew Morton wrote:

>
> On Thu, 3 Jul 2008 14:31:26 -0400 (EDT)
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
> > Due to a possible deadlock, the waking of the softirq was pushed outside
> > of the hrtimer base locks. See commit 0c96c5979a522c3323c30a078a70120e29b5bdbc
>
> Please quote at least the patch title rather than raw hashes.

Sorry, will do next time. I'm getting to use to git.

>
> afaict that patch isn't in 2.6.25 yet you copied stable@...nel.org.
> Please clarify.

The reason I did so is because that commit has a Cc: stable@...nel.org.
I figured that if that patch is in queue for stable this one should be in
right afterwards.

>
> >
> > 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.
> >
>
> This seems to be 2.6.26 material and is inapplicable to 2.6.25?
>

[/me goes to look at the 2.6.25.4 he has sitting around]

The above mentioned commit (Title: hrtimer: raise softirq unlocked to
avoid circular lock dependency) is, in fact, in 2.6.25.4.

-- Steve

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