linux-kernel - Re: dd/mke2fs on loopback hangs

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Date:	Tue, 06 Nov 2007 22:04:51 +0100
From:	Milan Broz <mbroz@...hat.com>
To:	linux-kernel@...r.kernel.org, list+2007@...kva.net
Subject: Re: dd/mke2fs on loopback hangs

Petar Bogdanovic wrote:
> I experience some strange problems with my loopback-on-ext3-setup.
> After creating a plain `zeroed' dummy-file and doing a /dev/loop/0 on
> it, every dd or mke2fs hangs while doing certain write()s. Here are the
> steps just in order to show, how simple the setup is:
...

> P.S:	$ uname -a
> 	Linux pintail 2.6.23-ARCH #1 SMP PREEMPT Sat Oct 27 09:04:14 UTC
> 	2007 i686 Intel(R) Pentium(R) M processor 1.70GHz GenuineIntel
> 	GNU/Linux

Hi Petar,

I saw similar bug report for dm-crypt over loop but reproducible even
on stand-alone loop devices -  see http://bugzilla.kernel.org/show_bug.cgi?id=8020

The problem was caused by loop io stalling in balance_dirty_pages.

Per BDI dirty limit patchset (included in 2.6.24-rc) fixed it.

Anyway, you should attach output of process states when system stops
responding (output of "echo t >/proc/sysrq-trigger" ) here to allow
some analysis.

Milan
--
mbroz@...hat.com


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