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Date: Sun, 18 Jan 2009 03:00:38 +0100
From: Johannes Weiner <hannes@cmpxchg.org>
To: Dave Jones <davej@redhat.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
       Andrea Righi <righi.andrea@gmail.com>
Subject: Re: .29rc2 lockdep report. fb_mmap vs sys_mmap2
Message-ID: <20090118020038.GA17489@cmpxchg.org>
References: <20090117231925.GA28055@redhat.com>
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On Sat, Jan 17, 2009 at 06:19:25PM -0500, Dave Jones wrote:
> Two mmaps enter! Fight!
> 
> 
>  =======================================================
>  [ INFO: possible circular locking dependency detected ]
>  2.6.29-0.41.rc2.fc11.i686 #1
>  -------------------------------------------------------
>  plymouthd/669 is trying to acquire lock:
>  (&fb_info->lock){--..}, at: [<c055355c>] fb_mmap+0x87/0x156
> 
>  but task is already holding lock:
>  (&mm->mmap_sem){----}, at: [<c0406a5d>] sys_mmap2+0x44/0x7b
> 
>  which lock already depends on the new lock.
> 
> 
>  the existing dependency chain (in reverse order) is:
> 
>  -> #1 (&mm->mmap_sem){----}:
>        [<c044fef3>] __lock_acquire+0x9af/0xb22
>        [<c04500c1>] lock_acquire+0x5b/0x81
>        [<c048e036>] might_fault+0x60/0x80
>        [<c053dedc>] copy_to_user+0x2c/0xfc
>        [<c05542cc>] fb_ioctl+0x247/0x338
>        [<c04b0c9f>] vfs_ioctl+0x22/0x69
>        [<c04b1214>] do_vfs_ioctl+0x46a/0x4a3
>        [<c04b128d>] sys_ioctl+0x40/0x5a
>        [<c0403b76>] syscall_call+0x7/0xb
>        [<ffffffff>] 0xffffffff
> 
>  -> #0 (&fb_info->lock){--..}:
>        [<c044fdc8>] __lock_acquire+0x884/0xb22
>        [<c04500c1>] lock_acquire+0x5b/0x81
>        [<c06e1b98>] __mutex_lock_common+0xd5/0x329
>        [<c06e1e84>] mutex_lock_nested+0x2e/0x36
>        [<c055355c>] fb_mmap+0x87/0x156
>        [<c0494620>] mmap_region+0x22b/0x43c
>        [<c0494aa2>] do_mmap_pgoff+0x271/0x2d1
>        [<c0406a73>] sys_mmap2+0x5a/0x7b
>        [<c0403b76>] syscall_call+0x7/0xb
>        [<ffffffff>] 0xffffffff
> 
>  other info that might help us debug this:
> 
>  1 lock held by plymouthd/669:
>  #0:  (&mm->mmap_sem){----}, at: [<c0406a5d>] sys_mmap2+0x44/0x7b
> 
>  stack backtrace:
>  Pid: 669, comm: plymouthd Not tainted 2.6.29-0.41.rc2.fc11.i686 #1
>  Call Trace:
>  [<c06e09b6>] ? printk+0xf/0x11
>  [<c044f32d>] print_circular_bug_tail+0x5d/0x68
>  [<c044fdc8>] __lock_acquire+0x884/0xb22
>  [<c04500c1>] lock_acquire+0x5b/0x81
>  [<c055355c>] ? fb_mmap+0x87/0x156
>  [<c06e1b98>] __mutex_lock_common+0xd5/0x329
>  [<c055355c>] ? fb_mmap+0x87/0x156
>  [<c06e1e84>] mutex_lock_nested+0x2e/0x36
>  [<c055355c>] ? fb_mmap+0x87/0x156
>  [<c055355c>] fb_mmap+0x87/0x156
>  [<c0494620>] mmap_region+0x22b/0x43c
>  [<c0494aa2>] do_mmap_pgoff+0x271/0x2d1
>  [<c0406a73>] sys_mmap2+0x5a/0x7b
>  [<c0403b76>] syscall_call+0x7/0xb

I reported this one already some time ago [1], Andrea Righi [cc'd]
also had a fix [2] but it seemed to not have made it in.  Andrea,
perhaps you can resend it?

	Hannes

[1] http://lkml.org/lkml/2008/10/22/759
[2] http://lkml.org/lkml/2008/10/28/377
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