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

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Message-Id: <E1PPaIw-0004pW-Mk@pomaz-ex.szeredi.hu>
Date:	Mon, 06 Dec 2010 13:36:30 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Michael Leun <lkml20101129@...ton.leun.net>
CC:	miklos@...redi.hu, 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 Fri, 3 Dec 2010, Michael Leun wrote:
> 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.

Thanks.

For you the workaround would be to use the "kernel_cache" option which
disables cache invalidation on open.

I'll try to reproduce the BUG on my machine, and if I don't succeed
I'll need som more help from you.

Also could you please send me your kernel .config

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

Probably just coincidence.  Sometimes the frequency a bug shows up
depends on code layout (and hence cache layout) differences, which can
vary from compile to compile and even from one boot to the next.

Thanks,
Miklos
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