Re: v2.6.26-rc7/cgroups: circular locking dependency

[Cyrill Gorcunov <gorcunov@gmail.com>]

[KOSAKI Motohiro - Mon, Jun 23, 2008 at 12:34:04AM +0900]
| CC'ed Paul Jackson
| 
| it seems typical ABBA deadlock.
| I think cpuset use cgrou_lock() by mistake.
| 
| IMHO, cpuset_handle_cpuhp() sholdn't use cgroup_lock() and
| shouldn't call rebuild_sched_domains().
| 
| 
|  -> #1 (cgroup_mutex){--..}:
|        [<c015a435>] __lock_acquire+0xf45/0x1040
|        [<c015a5c8>] lock_acquire+0x98/0xd0
|        [<c05416d1>] mutex_lock_nested+0xb1/0x300
|        [<c0160e6f>] cgroup_lock+0xf/0x20			   cgroup_lock
|        [<c0164750>] cpuset_handle_cpuhp+0x20/0x180
|        [<c014ea77>] notifier_call_chain+0x37/0x70
|        [<c014eae9>] __raw_notifier_call_chain+0x19/0x20
|        [<c051f8c8>] _cpu_down+0x78/0x240			cpu_hotplug.lock
|        [<c051fabb>] cpu_down+0x2b/0x40				  cpu_add_remove_lock
|        [<c0520cd9>] store_online+0x39/0x80
|        [<c02f627b>] sysdev_store+0x2b/0x40
|        [<c01d3372>] sysfs_write_file+0xa2/0x100
|        [<c0195486>] vfs_write+0x96/0x130
|        [<c0195b4d>] sys_write+0x3d/0x70
|        [<c010831b>] sysenter_past_esp+0x78/0xd1
|        [<ffffffff>] 0xffffffff
| 
|  -> #0 (&cpu_hotplug.lock){--..}:
|        [<c0159fe5>] __lock_acquire+0xaf5/0x1040
|        [<c015a5c8>] lock_acquire+0x98/0xd0
|        [<c05416d1>] mutex_lock_nested+0xb1/0x300
|        [<c015efbc>] get_online_cpus+0x2c/0x40			      cpu_hotplug.lock
|        [<c0163e6d>] rebuild_sched_domains+0x7d/0x3a0
|        [<c01653a4>] cpuset_common_file_write+0x204/0x440	cgroup_lock
|        [<c0162bc7>] cgroup_file_write+0x67/0x130
|        [<c0195486>] vfs_write+0x96/0x130
|        [<c0195b4d>] sys_write+0x3d/0x70
|        [<c010831b>] sysenter_past_esp+0x78/0xd1
|        [<ffffffff>] 0xffffffff
| 
| 
| > Hi,
| >
| > I decided to see what cgroups is all about, and followed the instructions
| > in Documentation/cgroups.txt :-) It happened when I did this:
| >
| >    [root@damson /dev/cgroup/Vegard 0]
| >    # echo 1 > cpuset.cpus
| >
| > I can also provide the kernel config if necessary.
| >
| >
| > Vegard
| >
| >
| >  =======================================================
| >  [ INFO: possible circular locking dependency detected ]
| >  2.6.26-rc7 #25
| >  -------------------------------------------------------
| >  bash/10032 is trying to acquire lock:
| >  (&cpu_hotplug.lock){--..}, at: [<c015efbc>] get_online_cpus+0x2c/0x40
| >
| >  but task is already holding lock:
| >  (cgroup_mutex){--..}, at: [<c0160e6f>] cgroup_lock+0xf/0x20
| >
| >  which lock already depends on the new lock.
| 

Thanks Kosaki!

		- Cyrill -