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Subject: Re: pstore: change mutex locking to spin_locks
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Luck, Tony" <tony.luck@intel.com>, linux-kernel@vger.kernel.org,
        Don Zickus <dzickus@redhat.com>, Matthew Garrett <mjg@redhat.com>,
        Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
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Date: Wed, 17 Aug 2011 23:47:59 +0200
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On Wed, 2011-08-17 at 14:22 -0700, Andrew Morton wrote:
> It's still bad if lockdep is enabled.  See
> kernel/lockdep.c:lock_acquire() and lock_release().  They aren't
> NMI-safe. 

Good thing nmi_enter() does lockdep_disable() and makes lock_acquire()
bail on if (current->lockdep_recursion).

Still the fact that pstore needs locks from NMI context (let alone tried
to use a mutex) makes one think one should avoid it like the plague.