Re: [PATCH] remove the BKL: remove "BKL auto-drop" assumption from nfs3_rpc_wrapper()
From: Alessio Igor Bogani
Date: Sun Apr 12 2009 - 16:34:41 EST
Dear Sir Molnar,
2009/4/12 Ingo Molnar <mingo@xxxxxxx>:
[...]
>> 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]
[ 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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