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

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Message-ID: <20110711215541.GF2938@redhat.com>
Date:	Mon, 11 Jul 2011 17:55:41 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"mjg@...hat.com" <mjg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ying.huang@...el.com
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.
> 
> So ... ideas (and patches) are most welcome.

I tested the spin_lock_irqsave thing on my one box where it was failing
and got past my initial problem into kdump.  So that is a positive and I
can post the patch for that.  Though it probably isn't a complete
solution, it is better than a mutex.

However, I have been scratching my head at a follow up problem, which is
when I inject an error which produces an NMI->GHES->panic, the error
record doesn't get stored under pstore (or maybe ERST too).  I do see the
ERST code follow all the correct steps in storing the kmsg_dump logs into
the ERST table.  Just on the reboot, when I mount pstore it isn't there.

When I perform an 'echo c > /proc/sysrq-trigger', it shows up on the
reboot.  Not sure what can be going wrong.  I cc'd Ying with hopes he
might have some thoughts.

Cheers,
Don
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