linux-kernel - Re: kernel BUG at mm/truncate.c:475!

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Date:	Fri, 3 Dec 2010 08:53:50 +0100
From:	Michael Leun <lkml20101129@...ton.leun.net>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	hughd@...gle.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: kernel BUG at mm/truncate.c:475!

On Thu, 2 Dec 2010 11:57:22 +0100
Michael Leun <lkml20101129@...ton.leun.net> wrote:

> > Can you please describe in detail the workload that's causing this
> > to happen?
> 
> Thats rather complicated, but I'll try. Basically it boils down to:
> 
> unshare -n -m /bin/bash
> unionfs -o
> cow,suid,allow_other,max_files=65536 /home/netenv/user1-union=RW:/=RO /home/netenv/user1
> mount -n -t proc none /home/netenv/user1/proc mount -n -t sysfs
> none /home/netenv/user1/sys mount -n -t devtmpfs
> devtmpfs /home/netenv/user1/dev mount -n -t devpts
> devpts /home/netenv/user1/dev/pts chroot /home/netenv/user1 /bin/su -
> user1
[...]
> In some of this setups two or more environments share the same
> writable branch, so the files in this environments changed against
> real root of the machine are the same, e.g.:
> 
> [...]
> unionfs -o
> cow,suid,allow_other,max_files=65536 /home/netenv/commondir=RW:/=RO /home/netenv/user1
> [...]
> 
> and another one
> 
> [...]
> unionfs -o
> cow,suid,allow_other,max_files=65536 /home/netenv/commondir=RW:/=RO /home/netenv/user2
> [...]

Additional note: Happens also WITHOUT that "two unionfs mounts use the
same branch dir" stuff.

Really seems to happen much more often in 2.6.36.1 than in 2.6.36.

> I observed that unionfs process takes much more cpu power than usual
> before fault happens.

This also happens without that "two unionfs mounts use the same branch
dir" stuff.

-- 
MfG,

Michael Leun

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