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    SubjectRe: v2.6.26-rc7/cgroups: circular locking dependency
    [Vegard Nossum - Sat, Jun 21, 2008 at 07:38:59PM +0200]
    | 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.
    |
    |
    | the existing dependency chain (in reverse order) is:
    |
    | -> #1 (cgroup_mutex){--..}:
    | [<c015a435>] __lock_acquire+0xf45/0x1040
    | [<c015a5c8>] lock_acquire+0x98/0xd0
    | [<c05416d1>] mutex_lock_nested+0xb1/0x300
    | [<c0160e6f>] cgroup_lock+0xf/0x20
    | [<c0164750>] cpuset_handle_cpuhp+0x20/0x180
    | [<c014ea77>] notifier_call_chain+0x37/0x70
    | [<c014eae9>] __raw_notifier_call_chain+0x19/0x20
    | [<c051f8c8>] _cpu_down+0x78/0x240
    | [<c051fabb>] cpu_down+0x2b/0x40
    | [<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
    | [<c0163e6d>] rebuild_sched_domains+0x7d/0x3a0
    | [<c01653a4>] cpuset_common_file_write+0x204/0x440
    | [<c0162bc7>] cgroup_file_write+0x67/0x130
    | [<c0195486>] vfs_write+0x96/0x130
    | [<c0195b4d>] sys_write+0x3d/0x70
    | [<c010831b>] sysenter_past_esp+0x78/0xd1
    | [<ffffffff>] 0xffffffff
    |
    | other info that might help us debug this:
    |
    | 1 lock held by bash/10032:
    | #0: (cgroup_mutex){--..}, at: [<c0160e6f>] cgroup_lock+0xf/0x20
    |
    | stack backtrace:
    | Pid: 10032, comm: bash Not tainted 2.6.26-rc7 #25
    | [<c0157ae7>] print_circular_bug_tail+0x77/0x90
    | [<c0159fe5>] __lock_acquire+0xaf5/0x1040
    | [<c015a5c8>] lock_acquire+0x98/0xd0
    | [<c015efbc>] ? get_online_cpus+0x2c/0x40
    | [<c05416d1>] mutex_lock_nested+0xb1/0x300
    | [<c015efbc>] ? get_online_cpus+0x2c/0x40
    | [<c015efbc>] ? get_online_cpus+0x2c/0x40
    | [<c015efbc>] get_online_cpus+0x2c/0x40
    | [<c0163e6d>] rebuild_sched_domains+0x7d/0x3a0
    | [<c0158e65>] ? mark_held_locks+0x65/0x80
    | [<c0190ac5>] ? kfree+0xb5/0x120
    | [<c027736a>] ? heap_free+0xa/0x10
    | [<c027736a>] ? heap_free+0xa/0x10
    | [<c01653a4>] cpuset_common_file_write+0x204/0x440
    | [<c0163c30>] ? started_after+0x0/0x70
    | [<c010e585>] ? native_sched_clock+0xb5/0x110
    | [<c0162e10>] ? started_after+0x0/0x70
    | [<c0164c80>] ? cpuset_test_cpumask+0x0/0x20
    | [<c0164ca0>] ? cpuset_change_cpumask+0x0/0x20
    | [<c0162bc7>] cgroup_file_write+0x67/0x130
    | [<c01651a0>] ? cpuset_common_file_write+0x0/0x440
    | [<c010e585>] ? native_sched_clock+0xb5/0x110
    | [<c0195486>] vfs_write+0x96/0x130
    | [<c0162b60>] ? cgroup_file_write+0x0/0x130
    | [<c0195b4d>] sys_write+0x3d/0x70
    | [<c010831b>] sysenter_past_esp+0x78/0xd1
    | =======================
    |

    Hi Vegard,

    would be interesting to see your config please

    - Cyrill -


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