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    SubjectRe: v2.6.26-rc7/cgroups: circular locking dependency
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    On Mon, 2008-06-23 at 00:34 +0900, KOSAKI Motohiro wrote:
    > 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().

    Looks like Max forgot to test with lockdep enabled...

    Well, someone should when you change the online map.

    Max, Paul, can we handle this in update_sched_domains() instead?

    > -> #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.
    > --
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