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Date: Sun, 14 Sep 2008 00:44:42 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <npiggin@suse.de>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [lockdep] possible circular locking, between &mm->mmap_sem and
 &dev->ev_mutex
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On Sun, 14 Sep 2008 09:39:06 +0200 Ingo Molnar <mingo@elte.hu> wrote:

> with the new mmap_sem lockdep annotations, -tip testing found a third 
> lockdep assert, see below. Config attached.
> 
> 	Ingo
> 
> ----------------->
> [ 6460.634452] 
> [ 6460.634465] =======================================================
> [ 6460.634494] [ INFO: possible circular locking dependency detected ]
> [ 6460.634517] 2.6.27-rc6-tip-00290-g8e229c3-dirty #1
> [ 6460.634535] -------------------------------------------------------
> [ 6460.634555] gdm-simple-gree/4778 is trying to acquire lock:
> [ 6460.634574]  (&mm->mmap_sem){----}, at: [<c018fe33>] might_fault+0x36/0x73
> [ 6460.634639] 
> [ 6460.634645] but task is already holding lock:
> [ 6460.634662]  (&dev->ev_mutex){--..}, at: [<c01c7a76>] inotify_read+0xd8/0x16e
> [ 6460.634715] 
> [ 6460.634721] which lock already depends on the new lock.

Yes, there's a thread in my intray called "inotify_read's ev_mutex vs
do_page_fault's mmap_sem...".  It's a bit flakey-looking, but there's a
patch in there.