linux-kernel - Re: pstore dump inside an nmi handler

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Message-ID: <20110708214941.GA20511@srcf.ucam.org>
Date:	Fri, 8 Jul 2011 22:49:41 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Don Zickus <dzickus@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: pstore dump inside an nmi handler

On Fri, Jul 08, 2011 at 02:40:13PM -0700, Luck, Tony wrote:
> > Inside pstore_dump(), the first thing it tries to grab is a mutex_lock()
> > (inside an nmi hander).  This seems to be the root cause of my problems.
> 
> Someone else pointed out that mutex_lock() is a problem here too. They
> wondered whether spin_lock_irqsave() would work - or whether pstore
> backends were allowed to sleep - to which I said I hoped they didn't,
> but wasn't really sure what the future will hold.

EFI can't sleep (at least, not as far as the kernel's concerned), so 
we're safe there. I think it's fair to assume atomicity here - crash 
dumping is a pretty specific situation. Although we may need to think 
about whether pstore should be saving reboot and poweroff in that case.

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