linux-kernel - Re: pstore: change mutex locking to spin

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Date:	Fri, 12 Aug 2011 18:59:12 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	linux-kernel@...r.kernel.org, Don Zickus <dzickus@...hat.com>
Subject: Re: pstore: change mutex locking to spin_locks

On Fri, Aug 12, 2011 at 10:54:51AM -0700, Luck, Tony wrote:
> From: Don Zickus <dzickus@...hat.com>
> 
> pstore was using mutex locking to protect read/write access to the
> backend plug-ins.  This causes problems when pstore is executed in
> an NMI context through panic() -> kmsg_dump().
> 
> This patch changes the mutex to a spin_lock_irqsave then also checks to
> see if we are in an NMI context.  If we are in an NMI and can't get the
> lock, just print a message stating that and blow by the locking.
> 
> All this is probably a hack around the bigger locking problem but it
> solves my current situation of trying to sleep in an NMI context.
> 
> Tested by loading the lkdtm module and executing a HARDLOCKUP which
> will cause the machine to panic inside the nmi handler.
> 
> Signed-off-by: Don Zickus <dzickus@...hat.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
Acked-by: Matthew Garrett <mjg@...hat.com>

-- 
Matthew Garrett | mjg59@...f.ucam.org
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