linux-kernel - Re: percpu related boot crash on x86

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Message-ID: <4D37F2C9.8000906@kernel.org>
Date:	Thu, 20 Jan 2011 10:31:05 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Tejun Heo <tj@...nel.org>, Pekka Enberg <penberg@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: percpu related boot crash on x86

On 1/20/11 1:11 AM, Ingo Molnar wrote:
>
> * Ingo Molnar<mingo@...e.hu>  wrote:
>
>> Btw., based on Peter's suggestion i tried the limit-bumping hack below - but it
>> did not help, the crash still triggers on 5%-10% of all randconfig bootups.
>
> I'm now running tests with MAXSMP forcibly disabled - and there are no crashes after
> 69 randconfig iteration. Before it would crash within 10 iterations.
>
> So it seems the MAXSMP sizing tests triggers a new percpu regression.

It needs CONFIG_DEBUG_PAGEALLOC to trigger. As the comment in 
vmap_debug_free_range() already says "it's going to be slow" I wonder if 
we could just hack around the problem by adding a

   if (!irqs_disabled())

guard around the debugging code to make vfree() always work with IRQs 
disabled.

			Pekka
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