linux-kernel - Re: [PATCH] softlockup: fix NMI hangs due to lock race

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Date:	Mon, 2 Jun 2008 12:39:31 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	a.p.zijlstra@...llo.nl
Subject: Re: [PATCH] softlockup: fix NMI hangs due to lock race - 2.6.26-rc
	regression


* Jason Wessel <jason.wessel@...driver.com> wrote:

> The touch_nmi_watchdog() routine on x86 ultimately calls 
> touch_softlockup_watchdog().  The problem is that to touch the 
> softlockup watchdog, the cpu_clock code has to be called which could 
> involve multiple cpu locks and can lead to a hard hang if one of the 
> locks is held by a processor that is not going to return anytime soon 
> (such as could be the case with kgdb or perhaps even with some other 
> kind of exception).
> 
> This patch causes the public version of the 
> touch_softlockup_watchdog() to defer the cpu clock access to a later 
> point.

applied to tip/core/softlockup and cherry-picked it into tip/core/urgent 
as well for v2.6.26 merge. Thanks,

	Ingo
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