linux-kernel - Re: BUG: drop_pagecache

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Message-ID: <20080318204646.GY155407@sgi.com>
Date:	Wed, 19 Mar 2008 07:46:46 +1100
From:	David Chinner <dgc@....com>
To:	Jan Kara <jack@...e.cz>
Cc:	David Chinner <dgc@....com>, lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: BUG: drop_pagecache_sb vs kjournald lockup

On Tue, Mar 18, 2008 at 02:43:26PM +0100, Jan Kara wrote:
> > 2.6.25-rc3, 4p ia64, ext3 root drive.
> > 
> > I was running an XFS stress test on one of the XFS partitions on
> > the machine (zero load on the root ext3 drive), when the system
> > locked up in kjournald with this on the console:
> > 
> > BUG: spinlock lockup on CPU#2, kjournald/2150, a000000100e022e0
> > 
>   <snip traces>

<snip other stuff>

> > Anyone know the reason why drop_pagecache_sb() uses such a brute-force
> > mechanism to free up clean page cache pages?
>   Yes, we know that drop_pagecache_sb() has locking issues but since it
> is intended to be used for debugging purposes only, nobody cared enough
> to fix it. Completely untested patch below if you dare to try ;)

It may be intended for debuging purposes, but it does get used in
production HPC environments (a lot!). I guess I've never seen this
lockup before because SGI customers don't use ext3, but they have
complained about the system "stopping" while drop_caches is executed.
This locking ..... strategy would explain it, though.

I'll try the patch, but I can't guarantee anything - I only saw this
lockup once in about 18 hours when dropping caches every 2 seconds.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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