linux-kernel - Re: XFS/md/blkdev warning (was Re: Linux 2.6.26-rc2)

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Message-ID: <alpine.LFD.1.10.0805171131000.3020@woody.linux-foundation.org>
Date:	Sat, 17 May 2008 11:37:35 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alistair John Strachan <alistair@...zero.co.uk>
cc:	Jens Axboe <jens.axboe@...cle.com>, xfs@....sgi.com,
	Neil Brown <neilb@...e.de>, Nick Piggin <npiggin@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: XFS/md/blkdev warning (was Re: Linux 2.6.26-rc2)



On Sat, 17 May 2008, Alistair John Strachan wrote:
>
> My guess is that when the kernel runs out of MemFree and starts reclaiming the 
> cache, something is deadlocking somewhere. Just doing a:
> 
> cat /dev/zero >/path/to/file

Do this on the console (and having a serial console or working netconsole 
is a wonderful thing to log it, because otherwise it will generally just 
scroll off the screen), and trigger SysRQ-w. That dumps all blocked tasks 
to the screen.

You may need to do

	echo 1 > /proc/sys/kernel/sysrq 

before that to enable it.

(Or if you have some things still running because they haevn't hit the 
lock that causes the deadlock, you can try

	echo w > /proc/sysrq-trigger

rather than the key combination).

			Linus
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