Ocfs2 devel - Apr 2007 - configfs: possible recursive locking detected

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Hi guys -

I recently rebuilt my mainline kernel with lockdep enabled since I've
been getting reports of reiserfs lockdep warnings. When I booted, I got
the following warning from configfs. I haven't done any triage at all on
it, but one of the shortcomings of lockdep IMO is the false positives.
The ones for reiserfs just need better annotation. There's no error
condition. This might be the same.

- -Jeff


============================================[ INFO: possible recursive locking
detected ]
2.6.21-rc7-git5-default #6
- ---------------------------------------------
o2cb_ctl/4278 is trying to acquire lock:
 (&sysfs_inode_imutex_key){--..}, at: [<ffffffff8839e865>]
configfs_add_file+0x35/0x66 [configfs]

but task is already holding lock:
 (&sysfs_inode_imutex_key){--..}, at: [<ffffffff8839f400>]
configfs_attach_group+0x58/0x19d [configfs]

other info that might help us debug this:
2 locks held by o2cb_ctl/4278:
 #0:  (&inode->i_mutex/1){--..}, at: [<ffffffff80251580>]
lookup_create+0x23/0x84
 #1:  (&sysfs_inode_imutex_key){--..}, at: [<ffffffff8839f400>]
configfs_attach_group+0x58/0x19d [configfs]

stack backtrace:

Call Trace:
 [<ffffffff80299c5a>] __lock_acquire+0x155/0xbe2
 [<ffffffff8839e865>] :configfs:configfs_add_file+0x35/0x66
 [<ffffffff8029a762>] lock_acquire+0x7b/0x9f
 [<ffffffff8839e865>] :configfs:configfs_add_file+0x35/0x66
 [<ffffffff8025d0d6>] __mutex_lock_slowpath+0xe1/0x263
 [<ffffffff8025e726>] _spin_unlock+0x17/0x20
 [<ffffffff8839e865>] :configfs:configfs_add_file+0x35/0x66
 [<ffffffff8839f333>] :configfs:configfs_attach_item+0x18b/0x200
 [<ffffffff8023d713>] d_rehash+0x23/0x44
 [<ffffffff8839f3c3>] :configfs:configfs_attach_group+0x1b/0x19d
 [<ffffffff8839f4a3>] :configfs:configfs_attach_group+0xfb/0x19d
 [<ffffffff8839f4b1>] :configfs:configfs_attach_group+0x109/0x19d
 [<ffffffff80299673>] trace_hardirqs_on+0x124/0x14f
 [<ffffffff8839fdd0>] :configfs:configfs_mkdir+0x1c7/0x268
 [<ffffffff802ce0c7>] vfs_mkdir+0xdb/0x14b
 [<ffffffff802ce58c>] sys_mkdirat+0x97/0xd8
 [<ffffffff80299673>] trace_hardirqs_on+0x124/0x14f
 [<ffffffff8025e262>] trace_hardirqs_on_thunk+0x35/0x37
 [<ffffffff8025711e>] system_call+0x7e/0x83

- --
Jeff Mahoney
SUSE Labs
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On Fri, Apr 27, 2007 at 11:52:31AM -0400, Jeff Mahoney
wrote:
> I recently rebuilt my mainline kernel with lockdep enabled since I've
> been getting reports of reiserfs lockdep warnings. When I booted, I got
> the following warning from configfs. I haven't done any triage at all
on
> it, but one of the shortcomings of lockdep IMO is the false positives.
> The ones for reiserfs just need better annotation. There's no error
> condition. This might be the same.
Without looking at the trace, I'm going to take a guess that it probably
just needs more annotation. There's a bunch of false positives in configfs
and ocfs2 right now which need fixing. I got a couple of them a while back,
but that didn't scratch the surface it seems :/
	--Mark

--
Mark Fasheh
Senior Software Developer, Oracle
mark.fasheh@oracle.com

On Fri, Apr 27, 2007 at 11:52:31AM -0400, Jeff Mahoney
wrote:
> I recently rebuilt my mainline kernel with lockdep enabled since I've
> been getting reports of reiserfs lockdep warnings. When I booted, I got
> the following warning from configfs. I haven't done any triage at all
on
> it, but one of the shortcomings of lockdep IMO is the false positives.
> The ones for reiserfs just need better annotation. There's no error
> condition. This might be the same.
	Without looking deeply, that stack is pretty much where we
expect to see recursive locking that needs annotation.  It's carefully
designed, but I haven't gotten around to learning how to annotate it.

Joel

-- 

"The doctrine of human equality reposes on this: that there is no
 man really clever who has not found that he is stupid."
	- Gilbert K. Chesterson

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127