From: Peter Zijlstra <peterz@infradead.org>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman <gregkh@suse.de>,
Kay Sievers <kay.sievers@vrfy.org>
Subject: Re: Lockdep problem involving sysfs_mutex in ext4 in linux-next
Date: Sun, 15 Mar 2009 00:05:08 +0100 [thread overview]
Message-ID: <1237071908.8939.788.camel@laptop> (raw)
In-Reply-To: <E1LiURX-0000jG-Lx@closure.thunk.org>
On Sat, 2009-03-14 at 10:02 -0400, Theodore Ts'o wrote:
> I'm occasionally seeing a circular locking dependency in linux-next when
> I unmount an ext4 filesystem, apparently involving sysfs_mutex in
> sysfs_addrm_start(), and I have no idea what's going on. Some help from
> kobject experts would be greatly appreciated. I assume I must be doing
> something wrong. I took the basic pattern from btrfs, but I suspect I
> may have broken some of the kobject lifetime rules when I adapted what I
> needed for ext4.
>
> It doesn't happen all the time, and it seems to be caused by how I'm
> releasing the ext4's sysfs kobject. In ext4_put_super():
>
> kobject_put(&sbi->s_kobj);
> wait_for_completion(&sbi->s_kobj_unregister);
Right that would require sysfs_mutex() while you're holding s_lock.
> The circular locking dependency is:
>
> [32667.071746] =======================================================
> [32667.071751] [ INFO: possible circular locking dependency detected ]
> [32667.071755] 2.6.29-rc7-00043-gafbc462 #11
> [32667.071758] -------------------------------------------------------
> [32667.071762] umount/2310 is trying to acquire lock:
> [32667.071764] (sysfs_mutex){--..}, at: [<c01f7130>] sysfs_addrm_start+0x28/0x9a
> [32667.071778]
> [32667.071779] but task is already holding lock:
> [32667.071782] (&type->s_lock_key#5){--..}, at: [<c01b752b>] lock_super+0x26/0x28
And here you snipped the interesting bit here it tells us how you
normally have the reverse lock order, namely:
sysfs_mutex.
s_lock
> [32667.072279] [<c01f7130>] ? sysfs_addrm_start+0x28/0x9a
> [32667.072284] [<c04c60ca>] __mutex_lock_common+0xdc/0x33a
> [32667.072289] [<c01f7130>] ? sysfs_addrm_start+0x28/0x9a
> [32667.072294] [<c04c63cf>] mutex_lock_nested+0x33/0x3b
> [32667.072300] [<c01f7130>] ? sysfs_addrm_start+0x28/0x9a
> [32667.072304] [<c01f7130>] sysfs_addrm_start+0x28/0x9a
> [32667.072309] [<c01f75ba>] sysfs_remove_dir+0x77/0xab
> [32667.072314] [<c02d5b2f>] kobject_del+0xf/0x2c
> [32667.072319] [<c02d5c80>] kobject_release+0x134/0x1cb
> [32667.072323] [<c02d5b4c>] ? kobject_release+0x0/0x1cb
> [32667.072328] [<c02d69e4>] kref_put+0x3c/0x4a
> [32667.072333] [<c02d5ac8>] kobject_put+0x37/0x3c
> [32667.072337] [<c021cd89>] ext4_put_super+0xab/0x215
> [32667.072342] [<c01b7fed>] generic_shutdown_super+0x62/0xe3
> [32667.072346] [<c01b8090>] kill_block_super+0x22/0x36
> [32667.072352] [<c01e6f52>] ? vfs_quota_off+0x0/0x17
> [32667.072357] [<c01b815b>] deactivate_super+0x5c/0x6f
> [32667.072361] [<c01c8c34>] mntput_no_expire+0xd4/0x106
> [32667.072366] [<c01c9138>] sys_umount+0x2a1/0x2c6
> [32667.072370] [<c01c916f>] sys_oldumount+0x12/0x14
> [32667.072375] [<c0117ff6>] syscall_call+0x7/0xb
> [32667.072380] [<c0110000>] ? x86_decode_insn+0x349/0xbc9
next prev parent reply other threads:[~2009-03-14 23:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-14 14:02 Lockdep problem involving sysfs_mutex in ext4 in linux-next Theodore Ts'o
2009-03-14 23:05 ` Peter Zijlstra [this message]
2009-03-20 22:25 ` Theodore Tso
2009-03-20 22:44 ` Theodore Tso
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