linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CALCETrUh_6tWdTyDwZ4U1BDSnN1khbGDGBvCTO3MVcdU-X23QA@mail.gmail.com>
Date:	Thu, 20 Nov 2014 15:55:09 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Tejun Heo <tj@...nel.org>
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 3:39 PM, Tejun Heo <tj@...nel.org> wrote:
> 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.  :(

That doesn't appear to have anything to with nmi though, right?

Wouldn't this issue be fixed by moving the vmalloc_fault check into
do_page_fault before exception_enter?

--Andy
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