On Wed, 22 Oct 2014, Steven Rostedt wrote:

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-> #1 (cpu_hotplug.lock#2){+.+.+.}:
        [<ffffffff81099fac>] lock_acquire+0xac/0x130
        [<ffffffff815b9f2c>] mutex_lock_nested+0x5c/0x3b0
        [<ffffffff81491892>] cpuidle_pause+0x12/0x30
        [<ffffffff81402314>] dpm_suspend_noirq+0x44/0x340
        [<ffffffff81402958>] dpm_suspend_end+0x38/0x80
        [<ffffffff810a07bd>] hibernation_snapshot+0xcd/0x370
        [<ffffffff810a1248>] hibernate+0x168/0x210
        [<ffffffff8109e9b4>] state_store+0xe4/0xf0
        [<ffffffff813003ef>] kobj_attr_store+0xf/0x20
        [<ffffffff8121e9a3>] sysfs_kf_write+0x43/0x60
        [<ffffffff8121e287>] kernfs_fop_write+0xe7/0x170
        [<ffffffff811a7342>] vfs_write+0xb2/0x1f0
        [<ffffffff811a7da4>] SyS_write+0x44/0xb0
        [<ffffffff815be856>] system_call_fastpath+0x16/0x1b

Yeah, this backtrace looks totally bogus. Unless there's some magic going on
with grabbing the get_online_cpus here?

Could you send your config. Maybe it has to do with some debug magic?

.config attached.

Can you reproduce this all the time? I tried this config and pm-suspend
and pm-hibernate, and they both worked fine without a single lockdep
splat.

Yes, it's 100% reliable for me.

-- 
Jiri Kosina
SUSE Labs