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Date: Mon, 13 Apr 2009 07:53:51 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Alessio Igor Bogani <abogani@texware.it>
Cc: Ingo Molnar <mingo@elte.hu>, Jonathan Corbet <corbet@lwn.net>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] remove the BKL: remove "BKL auto-drop" assumption from
	nfs3_rpc_wrapper()
Message-ID: <20090413055349.GA5986@nowhere>
References: <1239381281-11282-1-git-send-email-abogani@texware.it> <20090410182936.GA6018@nowhere> <63a49ef40904101350y68e93b85tad7d355868de9a38@mail.gmail.com> <20090412135912.GA5246@elte.hu> <63a49ef40904121334p6cd3179ag2a173665f2986ccb@mail.gmail.com>
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On Sun, Apr 12, 2009 at 10:34:28PM +0200, Alessio Igor Bogani wrote:
> Dear Sir Molnar,
> 
> 2009/4/12 Ingo Molnar <mingo@elte.hu>:
> [...]
> >> Unfortunately no. That lockdep message still happens when I
> >> unmount rpc_pipefs. I'll investigate further.
> >
> > might make sense to post that message here out in the open - maybe
> > someone with a strong NFSd-fu will comment on it.
> 
> This message appear when I unmount rpc_pipefs(/var/lib/nfs/rpc_pipefs)
> or nfsd (/proc/fs/nfsd):
> 
> [  130.094907] =======================================================
> [  130.096071] [ INFO: possible circular locking dependency detected ]
> [  130.096071] 2.6.30-rc1-nobkl #39
> [  130.096071] -------------------------------------------------------
> [  130.096071] umount/2883 is trying to acquire lock:
> [  130.096071]  (kernel_mutex){+.+.+.}, at: [<ffffffff80748074>]
> lock_kernel+0x34/0x43
> [  130.096071]
> [  130.096071] but task is already holding lock:
> [  130.096071]  (&type->s_lock_key#8){+.+...}, at:
> [<ffffffff803196ce>] lock_super+0x2e/0x30
> [  130.096071]
> [  130.096071] which lock already depends on the new lock.
> [  130.096071]


I have a very similar locking depency problem while unmounting reiserfs.
I haven't digged it yet because of a nasty hang with reiserfs I have to fix
first.

But I suspect this locking dependency is something to fix in the fs layer itself.

Frederic.


> [  130.096071]
> [  130.096071] the existing dependency chain (in reverse order) is:
> [  130.096071]
> [  130.096071] -> #2 (&type->s_lock_key#8){+.+...}:
> [  130.096071]        [<ffffffff802891cc>] __lock_acquire+0xf9c/0x13e0
> [  130.096071]        [<ffffffff8028972f>] lock_acquire+0x11f/0x170
> [  130.096071]        [<ffffffff8074534e>] __mutex_lock_common+0x5e/0x510
> [  130.096071]        [<ffffffff807458df>] mutex_lock_nested+0x3f/0x50
> [  130.096071]        [<ffffffff803196ce>] lock_super+0x2e/0x30
> [  130.096071]        [<ffffffff80319b8d>] __fsync_super+0x2d/0x90
> [  130.096071]        [<ffffffff80319c06>] fsync_super+0x16/0x30
> [  130.096071]        [<ffffffff80319c61>] do_remount_sb+0x41/0x280
> [  130.096071]        [<ffffffff8031ad1b>] get_sb_single+0x6b/0xe0
> [  130.096071]        [<ffffffffa00c3bdb>] nfsd_get_sb+0x1b/0x20 [nfsd]
> [  130.096071]        [<ffffffff8031a521>] vfs_kern_mount+0x81/0x180
> [  130.096071]        [<ffffffff8031a693>] do_kern_mount+0x53/0x110
> [  130.096071]        [<ffffffff8033504a>] do_mount+0x6ba/0x910
> [  130.096071]        [<ffffffff80335360>] sys_mount+0xc0/0xf0
> [  130.096071]        [<ffffffff80213232>] system_call_fastpath+0x16/0x1b
> [  130.096071]        [<ffffffffffffffff>] 0xffffffffffffffff
> [  130.096071]
> [  130.096071] -> #1 (&type->s_umount_key#34/1){+.+.+.}:
> [  130.096071]        [<ffffffff802891cc>] __lock_acquire+0xf9c/0x13e0
> [  130.096071]        [<ffffffff8028972f>] lock_acquire+0x11f/0x170
> [  130.096071]        [<ffffffff80277702>] down_write_nested+0x52/0x90
> [  130.096071]        [<ffffffff8031a99b>] sget+0x24b/0x560
> [  130.096071]        [<ffffffff8031acf3>] get_sb_single+0x43/0xe0
> [  130.096071]        [<ffffffffa00c3bdb>] nfsd_get_sb+0x1b/0x20 [nfsd]
> [  130.096071]        [<ffffffff8031a521>] vfs_kern_mount+0x81/0x180
> [  130.096071]        [<ffffffff8031a693>] do_kern_mount+0x53/0x110
> [  130.096071]        [<ffffffff8033504a>] do_mount+0x6ba/0x910
> [  130.096071]        [<ffffffff80335360>] sys_mount+0xc0/0xf0
> [  130.096071]        [<ffffffff80213232>] system_call_fastpath+0x16/0x1b
> [  130.096071]        [<ffffffffffffffff>] 0xffffffffffffffff
> [  130.096071]
> [  130.096071] -> #0 (kernel_mutex){+.+.+.}:
> [  130.096071]        [<ffffffff802892ad>] __lock_acquire+0x107d/0x13e0
> [  130.096071]        [<ffffffff8028972f>] lock_acquire+0x11f/0x170
> [  130.096071]        [<ffffffff8074534e>] __mutex_lock_common+0x5e/0x510
> [  130.096071]        [<ffffffff807458df>] mutex_lock_nested+0x3f/0x50
> [  130.096071]        [<ffffffff80748074>] lock_kernel+0x34/0x43
> [  130.096071]        [<ffffffff80319ef4>] generic_shutdown_super+0x54/0x140
> [  130.096071]        [<ffffffff8031a046>] kill_anon_super+0x16/0x50
> [  130.096071]        [<ffffffff8031a0a7>] kill_litter_super+0x27/0x30
> [  130.096071]        [<ffffffff8031a485>] deactivate_super+0x85/0xa0
> [  130.096071]        [<ffffffff8033301a>] mntput_no_expire+0x11a/0x160
> [  130.096071]        [<ffffffff803333d4>] sys_umount+0x64/0x3c0
> [  130.096071]        [<ffffffff80213232>] system_call_fastpath+0x16/0x1b
> [  130.096071]        [<ffffffffffffffff>] 0xffffffffffffffff
> [  130.096071]
> [  130.096071] other info that might help us debug this:
> [  130.096071]
> [  130.096071] 2 locks held by umount/2883:
> [  130.096071]  #0:  (&type->s_umount_key#35){+.+...}, at:
> [<ffffffff8031a47d>] deactivate_super+0x7d/0xa0
> [  130.096071]  #1:  (&type->s_lock_key#8){+.+...}, at:
> [<ffffffff803196ce>] lock_super+0x2e/0x30
> [  130.096071]
> [  130.096071] stack backtrace:
> [  130.096071] Pid: 2883, comm: umount Not tainted 2.6.30-rc1-nobkl #39
> [  130.096071] Call Trace:
> [  130.096071]  [<ffffffff80286c96>] print_circular_bug_tail+0xa6/0x100
> [  130.096071]  [<ffffffff802892ad>] __lock_acquire+0x107d/0x13e0
> [  130.096071]  [<ffffffff8028972f>] lock_acquire+0x11f/0x170
> [  130.096071]  [<ffffffff80748074>] ? lock_kernel+0x34/0x43
> [  130.096071]  [<ffffffff8074534e>] __mutex_lock_common+0x5e/0x510
> [  130.096071]  [<ffffffff80748074>] ? lock_kernel+0x34/0x43
> [  130.096071]  [<ffffffff80287685>] ? trace_hardirqs_on_caller+0x165/0x1c0
> [  130.096071]  [<ffffffff80748074>] ? lock_kernel+0x34/0x43
> [  130.096071]  [<ffffffff807458df>] mutex_lock_nested+0x3f/0x50
> [  130.096071]  [<ffffffff80748074>] lock_kernel+0x34/0x43
> [  130.096071]  [<ffffffff80319ef4>] generic_shutdown_super+0x54/0x140
> [  130.096071]  [<ffffffff8031a046>] kill_anon_super+0x16/0x50
> [  130.096071]  [<ffffffff8031a0a7>] kill_litter_super+0x27/0x30
> [  130.096071]  [<ffffffff8031a485>] deactivate_super+0x85/0xa0
> [  130.096071]  [<ffffffff8033301a>] mntput_no_expire+0x11a/0x160
> [  130.096071]  [<ffffffff803333d4>] sys_umount+0x64/0x3c0
> [  130.096071]  [<ffffffff80213232>] system_call_fastpath+0x16/0x1b
> 
> Please notice that removing lock_kernel()/unlock_kernel() from
> generic_shutdown_super() make this warning disappear but I'm not sure
> that is it the _real_ fix.
> 
> Ciao,
> Alessio

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