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

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Date:	Tue, 12 Jul 2011 11:34:36 -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 Mon, Jul 11, 2011 at 05:55:41PM -0400, Don Zickus wrote:
> 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.

Actually, is it expected that the ERST can handle only 8 records?  Also if
you remove those records with pstore mount under /mnt; 'rm -rf
/mnt/dmesg-*', are those records removed immediately or are they cached to
be removed later?  IOW, if a did a 'rm -rf ..' and then an 'echo c >
/proc/sysrq-trigger' immediately after it, would I expect those records to
be removed or not?  Testing shows they are removed on reboot but the later
'echo c > ..' didn't save any new error records. :-/

Cheers,
Don
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