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Re: 2.6.27-rc6: lockdep warning: iprune_mutex at shrink_icache_memory+0x

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: 2.6.27-rc6: lockdep warning: iprune_mutex at shrink_icache_memory+0x38/0x1a8
From: Grant Coady <grant_lkml@xxxxxxxxxxx>
Date: Tue, 16 Sep 2008 14:31:05 +1000
Cc: Alexander Beregalov <a.beregalov@xxxxxxxxx>, rjw@xxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, kernel-testers@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20080916025204.GL5811@disturbed>
Organization: http://bugsplatter.id.au/
References: <20080913233138.GA19576@orion> <20080916025204.GL5811@disturbed>
Reply-to: Grant Coady <gcoady.lk@xxxxxxxxx>
On Tue, 16 Sep 2008 12:52:04 +1000, Dave Chinner <david@xxxxxxxxxxxxx> wrote:

>On Sun, Sep 14, 2008 at 03:31:38AM +0400, Alexander Beregalov wrote:
>> Hi
>> 
>> [ INFO: possible circular locking dependency detected ]
>> 2.6.27-rc6-00034-gd1c6d2e #3
>> -------------------------------------------------------
>> nfsd/1766 is trying to acquire lock:
>>  (iprune_mutex){--..}, at: [<c01743fb>] shrink_icache_memory+0x38/0x1a8
>> 
>>  but task is already holding lock:
>>   (&(&ip->i_iolock)->mr_lock){----}, at: [<c021134f>]
>>   xfs_ilock+0xa2/0xd6
>> 
>> 
>> I read files through nfs and saw delay for few seconds.
>> System is x86_32, nfs, xfs.
>> The last working kernel is 2.6.27-rc5,
>> I do not know yet is it reproducible or not.
>
><sigh>
>
>We need a FAQ for this one. It's a false positive.  Google for an
>explanation - I've explained it 4 or 5 times in the past year and
>asked that the lockdep folk invent a special annotation for the
>iprune_mutex (or memory reclaim) because of the way it can cause
>recursion into the filesystem and hence invert lock orders without
>causing deadlocks.....

Yeah, but a 30 second dreadlock?  It's a long wait wondering what's 
gone down or not ;)

Grant.

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