lockdep splat in CPU hotplug

[Jiri Kosina]

Hi,

I am seeing the lockdep report below when resuming from suspend-to-disk 
with current Linus' tree (c2661b80609).

The reason for CCing Ingo and Peter is that I can't make any sense of one 
of the stacktraces lockdep is providing.

Please have a look at the very first stacktrace in the dump, where lockdep 
is trying to explain where cpu_hotplug.lock#2 has been acquired. It seems 
to imply that cpuidle_pause() is taking cpu_hotplug.lock, but that's not 
the case at all.

What am I missing?

Thanks.


 ======================================================
 [ INFO: possible circular locking dependency detected ]
 3.18.0-rc1-00069-gc2661b8 #1 Not tainted
 -------------------------------------------------------
 do_s2disk/2367 is trying to acquire lock:
  (cpuidle_lock){+.+.+.}, at: [<ffffffff814916c2>] cpuidle_pause_and_lock+0x12/0x20
 
but task is already holding lock:
  (cpu_hotplug.lock#2){+.+.+.}, at: [<ffffffff810522ea>] cpu_hotplug_begin+0x4a/0x80
 
which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #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
 
-> #0 (cpuidle_lock){+.+.+.}:
        [<ffffffff81099433>] __lock_acquire+0x1a03/0x1e30
        [<ffffffff81099fac>] lock_acquire+0xac/0x130
        [<ffffffff815b9f2c>] mutex_lock_nested+0x5c/0x3b0
        [<ffffffff814916c2>] cpuidle_pause_and_lock+0x12/0x20
        [<ffffffffc02e184c>] acpi_processor_hotplug+0x45/0x8a [processor]
        [<ffffffffc02df25a>] acpi_cpu_soft_notify+0xad/0xe3 [processor]
        [<ffffffff81071393>] notifier_call_chain+0x53/0xa0
        [<ffffffff810713e9>] __raw_notifier_call_chain+0x9/0x10
        [<ffffffff810521ce>] cpu_notify+0x1e/0x40
        [<ffffffff810524a8>] _cpu_up+0x148/0x160
        [<ffffffff815a7b99>] enable_nonboot_cpus+0xc9/0x1d0
        [<ffffffff810a0955>] hibernation_snapshot+0x265/0x370
        [<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
 
other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(cpu_hotplug.lock#2);
                                lock(cpuidle_lock);
                                lock(cpu_hotplug.lock#2);
   lock(cpuidle_lock);
 
 *** DEADLOCK ***

 8 locks held by do_s2disk/2367:
  #0:  (sb_writers#6){.+.+.+}, at: [<ffffffff811a7443>] vfs_write+0x1b3/0x1f0
  #1:  (&of->mutex){+.+.+.}, at: [<ffffffff8121e25b>] kernfs_fop_write+0xbb/0x170
  #2:  (s_active#188){.+.+.+}, at: [<ffffffff8121e263>] kernfs_fop_write+0xc3/0x170
  #3:  (pm_mutex){+.+.+.}, at: [<ffffffff810a112e>] hibernate+0x4e/0x210
  #4:  (device_hotplug_lock){+.+.+.}, at: [<ffffffff813f1b52>] lock_device_hotplug+0x12/0x20
  #5:  (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff815a7aef>] enable_nonboot_cpus+0x1f/0x1d0
  #6:  (cpu_hotplug.lock){++++++}, at: [<ffffffff810522a0>] cpu_hotplug_begin+0x0/0x80
  #7:  (cpu_hotplug.lock#2){+.+.+.}, at: [<ffffffff810522ea>] cpu_hotplug_begin+0x4a/0x80
 
stack backtrace:
 CPU: 1 PID: 2367 Comm: do_s2disk Not tainted 3.18.0-rc1-00069-g4da0564 #1
 Hardware name: LENOVO 7470BN2/7470BN2, BIOS 6DET38WW (2.02 ) 12/19/2008
  ffffffff823e4330 ffff8800789e7a48 ffffffff815b6754 0000000000001a69
  ffffffff823e4330 ffff8800789e7a98 ffffffff815b078b ffff8800741a5510
  ffff8800789e7af8 ffff8800741a5ea8 5a024e919538010b ffff8800741a5ea8
 Call Trace:
  [<ffffffff815b6754>] dump_stack+0x4e/0x68
  [<ffffffff815b078b>] print_circular_bug+0x203/0x214
  [<ffffffff81099433>] __lock_acquire+0x1a03/0x1e30
  [<ffffffff8109766d>] ? trace_hardirqs_on_caller+0xfd/0x1c0
  [<ffffffff81099fac>] lock_acquire+0xac/0x130
  [<ffffffff814916c2>] ? cpuidle_pause_and_lock+0x12/0x20
  [<ffffffff815b9f2c>] mutex_lock_nested+0x5c/0x3b0
  [<ffffffff814916c2>] ? cpuidle_pause_and_lock+0x12/0x20
  [<ffffffff814916c2>] cpuidle_pause_and_lock+0x12/0x20
  [<ffffffffc02e184c>] acpi_processor_hotplug+0x45/0x8a [processor]
  [<ffffffffc02df25a>] acpi_cpu_soft_notify+0xad/0xe3 [processor]
  [<ffffffff81071393>] notifier_call_chain+0x53/0xa0
  [<ffffffff810713e9>] __raw_notifier_call_chain+0x9/0x10
  [<ffffffff810521ce>] cpu_notify+0x1e/0x40
  [<ffffffff810524a8>] _cpu_up+0x148/0x160
  [<ffffffff815a7b99>] enable_nonboot_cpus+0xc9/0x1d0
  [<ffffffff810a0955>] hibernation_snapshot+0x265/0x370
  [<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
  [<ffffffff815be87b>] ? sysret_check+0x1b/0x56
  [<ffffffff811a7da4>] SyS_write+0x44/0xb0
  [<ffffffff815be856>] system_call_fastpath+0x16/0x1b

-- 
Jiri Kosina
SUSE Labs
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