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

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Message-Id: <20110708.144846.2266757026673899391.davem@davemloft.net>
Date:	Fri, 08 Jul 2011 14:48:46 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	tony.luck@...el.com
Cc:	dzickus@...hat.com, mjg@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: pstore dump inside an nmi handler

From: "Luck, Tony" <tony.luck@...el.com>
Date: Fri, 8 Jul 2011 14:40:13 -0700

>> 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.
> 
> So ... ideas (and patches) are most welcome.

Probably you'll need to queue things atomically using something
based upon cmpxchg() like the generic ring buffer does.
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