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    SubjectRe: [PULL] cpumask tree

    * Mike Travis <travis@sgi.com> wrote:

    > Ingo Molnar wrote:
    > > * Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > >> i suspect it's:
    > >>
    > >> | commit 2d22bd5e74519854458ad372a89006e65f45e628
    > >> | Author: Mike Travis <travis@sgi.com>
    > >> | Date: Wed Dec 31 18:08:46 2008 -0800
    > >> |
    > >> | x86: cleanup remaining cpumask_t code in microcode_core.c
    > >>
    > >> as the microcode is loaded during CPU onlining.
    > >
    > > yep, that's the bad one. Should i revert it or do you have a safe fix in
    > > mind?
    > >
    > > Ingo
    >
    > Probably revert for now. There are a few more following patches that
    > also use 'work_on_cpu' so a better (more global?) fix should be used.
    >
    > Any thought on using a recursive lock for cpu-hotplug-lock? (At least
    > for get_online_cpus()?)

    but the problem has nothing to do with self-recursion. Take a look at the
    lockdep warning i posted (also below) - the locks are simply taken in the
    wrong order.

    your change adds this cpu_hotplug.lock usage:

    [ 43.652000] -> #1 (&cpu_hotplug.lock){--..}:
    [ 43.652000] [<ffffffff8027a7c0>] __lock_acquire+0xf10/0x1360
    [ 43.652000] [<ffffffff8027aca9>] lock_acquire+0x99/0xd0
    [ 43.652000] [<ffffffff809b5e4a>] __mutex_lock_common+0xaa/0x450
    [ 43.652000] [<ffffffff809b62cf>] mutex_lock_nested+0x3f/0x50
    [ 43.652000] [<ffffffff802516ba>] get_online_cpus+0x3a/0x50
    [ 43.652000] [<ffffffff802648dc>] work_on_cpu+0x6c/0xc0
    [ 43.652000] [<ffffffff8022b2a2>] mc_sysdev_add+0x92/0xa0
    [ 43.652000] [<ffffffff8050a800>] sysdev_driver_register+0xb0/0x140
    [ 43.652000] [<ffffffff8163c792>] microcode_init+0xb2/0x13b
    [ 43.652000] [<ffffffff8020a041>] do_one_initcall+0x41/0x180
    [ 43.652000] [<ffffffff8162e6cb>] kernel_init+0x145/0x19d
    [ 43.652000] [<ffffffff802146aa>] child_rip+0xa/0x20
    [ 43.652000] [<ffffffffffffffff>] 0xffffffffffffffff

    which nests the inside sysdev_drivers_lock - which is wrong
    [sysdev_drivers_lock is a pretty lowlevel lock that generally nests inside
    the CPU hotplug lock].

    If you want to use work_on_cpu() it should be done on a higher level, so
    that sysdev_drivers_lock is taken after the hotplug lock.

    Ingo

    [ 43.376051] lockdep: fixing up alternatives.
    [ 43.380007] SMP alternatives: switching to UP code
    [ 43.616014] CPU0 attaching NULL sched-domain.
    [ 43.620068] CPU1 attaching NULL sched-domain.
    [ 43.644482] CPU0 attaching NULL sched-domain.
    [ 43.648264]
    [ 43.648265] =======================================================
    [ 43.652000] [ INFO: possible circular locking dependency detected ]
    [ 43.652000] 2.6.28-05081-geeff031-dirty #37
    [ 43.652000] -------------------------------------------------------
    [ 43.652000] S99local/1238 is trying to acquire lock:
    [ 43.652000] (sysdev_drivers_lock){--..}, at: [<ffffffff8050a52d>] sysdev_unregister+0x1d/0x80
    [ 43.652000]
    [ 43.652000] but task is already holding lock:
    [ 43.652000] (&cpu_hotplug.lock){--..}, at: [<ffffffff802515d7>] cpu_hotplug_begin+0x27/0x60
    [ 43.652000]
    [ 43.652000] which lock already depends on the new lock.
    [ 43.652000]
    [ 43.652000]
    [ 43.652000] the existing dependency chain (in reverse order) is:
    [ 43.652000]
    [ 43.652000] -> #1 (&cpu_hotplug.lock){--..}:
    [ 43.652000] [<ffffffff8027a7c0>] __lock_acquire+0xf10/0x1360
    [ 43.652000] [<ffffffff8027aca9>] lock_acquire+0x99/0xd0
    [ 43.652000] [<ffffffff809b5e4a>] __mutex_lock_common+0xaa/0x450
    [ 43.652000] [<ffffffff809b62cf>] mutex_lock_nested+0x3f/0x50
    [ 43.652000] [<ffffffff802516ba>] get_online_cpus+0x3a/0x50
    [ 43.652000] [<ffffffff802648dc>] work_on_cpu+0x6c/0xc0
    [ 43.652000] [<ffffffff8022b2a2>] mc_sysdev_add+0x92/0xa0
    [ 43.652000] [<ffffffff8050a800>] sysdev_driver_register+0xb0/0x140
    [ 43.652000] [<ffffffff8163c792>] microcode_init+0xb2/0x13b
    [ 43.652000] [<ffffffff8020a041>] do_one_initcall+0x41/0x180
    [ 43.652000] [<ffffffff8162e6cb>] kernel_init+0x145/0x19d
    [ 43.652000] [<ffffffff802146aa>] child_rip+0xa/0x20
    [ 43.652000] [<ffffffffffffffff>] 0xffffffffffffffff
    [ 43.652000]
    [ 43.652000] -> #0 (sysdev_drivers_lock){--..}:
    [ 43.652000] [<ffffffff8027a89c>] __lock_acquire+0xfec/0x1360
    [ 43.652000] [<ffffffff8027aca9>] lock_acquire+0x99/0xd0
    [ 43.652000] [<ffffffff809b5e4a>] __mutex_lock_common+0xaa/0x450
    [ 43.652000] [<ffffffff809b62cf>] mutex_lock_nested+0x3f/0x50
    [ 43.652000] [<ffffffff8050a52d>] sysdev_unregister+0x1d/0x80
    [ 43.652000] [<ffffffff809af9d1>] mce_cpu_callback+0xce/0x101
    [ 43.652000] [<ffffffff809bbb75>] notifier_call_chain+0x65/0xa0
    [ 43.652000] [<ffffffff8026d696>] raw_notifier_call_chain+0x16/0x20
    [ 43.652000] [<ffffffff80964a00>] _cpu_down+0x240/0x350
    [ 43.652000] [<ffffffff80964b8b>] cpu_down+0x7b/0xa0
    [ 43.652000] [<ffffffff80966268>] store_online+0x48/0xa0
    [ 43.652000] [<ffffffff80509e90>] sysdev_store+0x20/0x30
    [ 43.652000] [<ffffffff80335ddf>] sysfs_write_file+0xcf/0x140
    [ 43.652000] [<ffffffff802dc1f7>] vfs_write+0xc7/0x150
    [ 43.652000] [<ffffffff802dc375>] sys_write+0x55/0x90
    [ 43.652000] [<ffffffff802133ca>] system_call_fastpath+0x16/0x1b
    [ 43.652000] [<ffffffffffffffff>] 0xffffffffffffffff
    [ 43.652000]
    [ 43.652000] other info that might help us debug this:
    [ 43.652000]
    [ 43.652000] 3 locks held by S99local/1238:
    [ 43.652000] #0: (&buffer->mutex){--..}, at: [<ffffffff80335d58>] sysfs_write_file+0x48/0x140
    [ 43.652000] #1: (cpu_add_remove_lock){--..}, at: [<ffffffff80964b3f>] cpu_down+0x2f/0xa0
    [ 43.652000] #2: (&cpu_hotplug.lock){--..}, at: [<ffffffff802515d7>] cpu_hotplug_begin+0x27/0x60
    [ 43.652000]
    [ 43.652000] stack backtrace:
    [ 43.652000] Pid: 1238, comm: S99local Not tainted 2.6.28-05081-geeff031-dirty #37
    [ 43.652000] Call Trace:
    [ 43.652000] [<ffffffff80277f24>] print_circular_bug_tail+0xa4/0x100
    [ 43.652000] [<ffffffff8027a89c>] __lock_acquire+0xfec/0x1360
    [ 43.652000] [<ffffffff8027aca9>] lock_acquire+0x99/0xd0
    [ 43.652000] [<ffffffff8050a52d>] ? sysdev_unregister+0x1d/0x80
    [ 43.652000] [<ffffffff809b5e4a>] __mutex_lock_common+0xaa/0x450
    [ 43.652000] [<ffffffff8050a52d>] ? sysdev_unregister+0x1d/0x80
    [ 43.652000] [<ffffffff8050a52d>] ? sysdev_unregister+0x1d/0x80
    [ 43.652000] [<ffffffff809b62cf>] mutex_lock_nested+0x3f/0x50
    [ 43.652000] [<ffffffff8050a52d>] sysdev_unregister+0x1d/0x80
    [ 43.652000] [<ffffffff809af9d1>] mce_cpu_callback+0xce/0x101
    [ 43.652000] [<ffffffff809bbb75>] notifier_call_chain+0x65/0xa0
    [ 43.652000] [<ffffffff8026d696>] raw_notifier_call_chain+0x16/0x20
    [ 43.652000] [<ffffffff80964a00>] _cpu_down+0x240/0x350
    [ 43.652000] [<ffffffff809b4763>] ? wait_for_common+0xe3/0x1b0
    [ 43.652000] [<ffffffff80964b8b>] cpu_down+0x7b/0xa0
    [ 43.652000] [<ffffffff80966268>] store_online+0x48/0xa0
    [ 43.652000] [<ffffffff80509e90>] sysdev_store+0x20/0x30
    [ 43.652000] [<ffffffff80335ddf>] sysfs_write_file+0xcf/0x140
    [ 43.652000] [<ffffffff802dc1f7>] vfs_write+0xc7/0x150
    [ 43.652000] [<ffffffff802dc375>] sys_write+0x55/0x90
    [ 43.652000] [<ffffffff802133ca>] system_call_fastpath+0x16/0x1b
    [ 43.652104] device: 'msr1': device_unregister
    [ 43.656005] PM: Removing info for No Bus:msr1


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