linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Wed, 26 Nov 2014 06:24:52 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	the arch/x86 maintainers <x86@...nel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: frequent lockups in 3.18rc4

On 11/26/2014 06:09 AM, Linus Torvalds wrote:
>
> On Nov 25, 2014 8:39 PM, "Jürgen Groß" <jgross@...e.com
> <mailto:jgross@...e.com>> wrote:
>  >
>  > I COULD trigger it with 3.17. Took much longer, but I've seen it once.
>  > And from Xen hypervisor data it was clear it was the same bug (cpu
>  > spinning in pmd_lock()).
>
> I'm still hoping you can give a back trace. I'd like to know what access
> it is that can trigger this, and preferably what the call chain to it was...

Working on it. Triggering it via sysrq(l) isn't working: machine hung
up. I'll try a dump, but this might take some time due to the machine
size...

If this isn't working I can always modify the hypervisor to show me
more of the kernel stack in that situation. This will be a pure dump,
but it should be possible to extract the back trace from that.

>
> I do believe it happened in 3.17, I just want to understand the but more
> - not just apply the fix..

Sure.

>
> Most of Dave's lockup back traces did not have the whole page fault in
> them, so while Dave has seen this too, there might be different symptoms...

Stay tuned... :-)


Juergen

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