linux-kernel - Re: 3.8-rc2: lockdep is complaining about mm_take_all

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Message-ID: <alpine.LNX.2.00.1301041639130.9143@pobox.suse.cz>
Date:	Fri, 4 Jan 2013 16:39:51 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: 3.8-rc2: lockdep is complaining about mm_take_all_locks()

On Fri, 4 Jan 2013, Jiri Kosina wrote:

> This is almost certainly because
> 
> commit 5a505085f043e8380f83610f79642853c051e2f1
> Author: Ingo Molnar <mingo@...nel.org>
> Date:   Sun Dec 2 19:56:46 2012 +0000
> 
>     mm/rmap: Convert the struct anon_vma::mutex to an rwsem
> 
> did this to mm_take_all_locks():
> 
> 	-               mutex_lock_nest_lock(&anon_vma->root->mutex, &mm->mmap_sem);
> 	+               down_write(&anon_vma->root->rwsem);
> 
> killing the lockdep annotation that has been there since 
> 
> commit 454ed842d55740160334efc9ad56cfef54ed37bc
> Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date:   Mon Aug 11 09:30:25 2008 +0200
> 
>     lockdep: annotate mm_take_all_locks()
> 
> The locking is obviously correct due to mmap_sem being held throughout the 
> whole operation, but I am not completely sure how to annotate this 
> properly for lockdep in down_write() case though. Ingo, please?

OK, I think the only solution is to introduce down_read_nest_lock(). I 
will prepare a patch.

-- 
Jiri Kosina
SUSE Labs
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