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Date: Tue, 22 Feb 2005 01:18:21 -0800
From: Andrew Morton <akpm@osdl.org>
To: "Thomas S. Iversen" <zensonic@zensonic.dk>
Cc: dm-devel@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: Help tracking down problem --- endless loop in
 __find_get_block_slow
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"Thomas S. Iversen" <zensonic@zensonic.dk> wrote:
>
> But if I do
> 
>  dd if=/dev/zero of=/mnt/testfile count=N, N>6
> 
>  I get into an endless loop in __find_get_block_slow. 

The only way in which __find_get_block_slow() can loop is if something
wrecked the buffer_head ring at page->private: something caused an internal
loop via bh->b_this_page.

Are you sure that's where things are hanging?  That it's not stuck on a
spinlock?

A sysrq-P trace might help.