[Ocfs2-devel] ocfs2: Possible deadlock in dlm?

[Tao Ma]

Hi Sunil/Joel,
	I just got a lockdep warning today when I enable it to
reflink check.

So the question is that dlm_domain_lock and dlm->spinlock are
spin_locked in different order.

In dlm_run_purge_list, we lock dlm->spinlock first and then in
dlm_lockres_release->dlm_put we lock dlm_domain_lock.
While in dlm_mark_domain_leaving we use the reverse order.

So is this a problem or these 2 scenarios can never happen together?
I have attached the lockdep print below.

Regards,
Tao

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.33-rc6 #2
-------------------------------------------------------
umount/3880 is trying to acquire lock:
 (&(&dlm->spinlock)->rlock){+.+...}, at: [<ffffffffa045c6e0>] dlm_unregister_domain+0x465/0x7ce [ocfs2_dlm]

but task is already holding lock:
 (dlm_domain_lock){+.+...}, at: [<ffffffffa045c6d7>] dlm_unregister_domain+0x45c/0x7ce [ocfs2_dlm]

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (dlm_domain_lock){+.+...}:
       [<ffffffff82065a01>] validate_chain+0xa40/0xd38
       [<ffffffff820664a6>] __lock_acquire+0x7ad/0x813
       [<ffffffff820665d3>] lock_acquire+0xc7/0xe4
       [<ffffffff8233d3da>] _raw_spin_lock+0x31/0x66
       [<ffffffffa045bf74>] dlm_put+0x1f/0x3e [ocfs2_dlm]
       [<ffffffffa046b6f6>] dlm_lockres_release+0x132/0x30e [ocfs2_dlm]
       [<ffffffff8218bbea>] kref_put+0x43/0x4f
       [<ffffffffa046999d>] dlm_lockres_put+0x14/0x16 [ocfs2_dlm]
       [<ffffffffa0460277>] dlm_run_purge_list+0x494/0x4df [ocfs2_dlm]
       [<ffffffffa04605c7>] dlm_thread+0x9d/0xe32 [ocfs2_dlm]
       [<ffffffff82054d4d>] kthread+0x7d/0x85
       [<ffffffff82003794>] kernel_thread_helper+0x4/0x10

-> #0 (&(&dlm->spinlock)->rlock){+.+...}:
       [<ffffffff820656ed>] validate_chain+0x72c/0xd38
       [<ffffffff820664a6>] __lock_acquire+0x7ad/0x813
       [<ffffffff820665d3>] lock_acquire+0xc7/0xe4
       [<ffffffff8233d3da>] _raw_spin_lock+0x31/0x66
       [<ffffffffa045c6e0>] dlm_unregister_domain+0x465/0x7ce [ocfs2_dlm]
       [<ffffffffa04941d5>] o2cb_cluster_disconnect+0x38/0x4a [ocfs2_stack_o2cb]
       [<ffffffffa04012ba>] ocfs2_cluster_disconnect+0x2a/0x4e [ocfs2_stackglue]
       [<ffffffffa04e95f4>] ocfs2_dlm_shutdown+0xf9/0x167 [ocfs2]
       [<ffffffffa051f606>] ocfs2_dismount_volume+0x1d8/0x39e [ocfs2]
       [<ffffffffa051fbe8>] ocfs2_put_super+0x88/0xf4 [ocfs2]
       [<ffffffff820dcc6d>] generic_shutdown_super+0x58/0xcc
       [<ffffffff820dcd03>] kill_block_super+0x22/0x3a
       [<ffffffffa051d671>] ocfs2_kill_sb+0x77/0x7f [ocfs2]
       [<ffffffff820dd438>] deactivate_super+0x68/0x7d
       [<ffffffff820f11ba>] mntput_no_expire+0x75/0xb0
       [<ffffffff820f172a>] sys_umount+0x2c2/0x321
       [<ffffffff8200296b>] system_call_fastpath+0x16/0x1b

other info that might help us debug this: