linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141120233920.GC25393@htj.dyndns.org>
Date:	Thu, 20 Nov 2014 18:39:20 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>, Don Zickus <dzickus@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: frequent lockups in 3.18rc4

On Thu, Nov 20, 2014 at 03:08:03PM -0800, Andy Lutomirski wrote:
> > So, for now, all we need is adding nmi check in percpu accessors,
> > right?
> >
> 
> What's the issue with nmi?  Page faults are supposed to nest correctly
> inside nmi, right?

Thought they couldn't.  Looking at the trace that Frederic linked, it
looks like straight-out tracing function recursion due to an
unexpected fault while holding a lock.  I don't think this can be
annotated from percpu accessor side.  There's nothing special about
the context.  :(

Does this matter for anybody other than tracers?  Ultimately, the
solution would be removing the vmalloc area faulting as Thomas
suggested.

Thanks.

-- 
tejun
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