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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Tue, 18 Oct 2011 13:12:41 -0700
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Subject: Re: Linux 3.1-rc9
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Simon Kirby <sim@hostway.ca>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Jones <davej@redhat.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Ingo Molnar <mingo@elte.hu>, David Miller <davem@davemloft.net>
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On Tue, Oct 18, 2011 at 12:48 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> It does not look related.

Yeah, the only lock held there seems to be the socket lock, and it
looks like all CPU's are spinning on it.

> Could you try to reproduce that problem with
> lockdep enabled? lockdep might make it go away, but it's definitely
> worth a try.

And DEBUG_SPINLOCK / DEBUG_SPINLOCK_SLEEP too. Maybe you're triggering
some odd networking thing.  It sounds unlikely, but maybe some error
case you get into doesn't release the socket lock.

I think PROVE_LOCKING already enables DEBUG_SPINLOCK, but the sleeping
lock thing is separate, iirc.

                    Linus