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

From: Linus Torvalds
Date: Sat May 17 2008 - 14:38:33 EST

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).

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