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Date:	Tue, 3 Apr 2012 06:06:44 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, kvm <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: kvm: RCU warning in async pf

On Mon, Apr 02, 2012 at 08:54:32PM -0400, Sasha Levin wrote:
> Hi all,
> 
> I got the spew at the bottom of the mail in a KVM guest using the KVM tools and running trinity.
> 
> I'm not quite sure how default_idle managed to trigger a pagefault, so that part looks odd to me.

Wrapping the offending RCU read-side critical section in RCU_NONIDLE()
is the intended solution -- though that assumes that you can tell where
the page fault will occur.

							Thanx, Paul

> [12140.220507] ===============================
> [12140.220507] [ INFO: suspicious RCU usage. ]
> [12140.220507] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.220507] -------------------------------
> [12140.220507] include/linux/rcupdate.h:729 rcu_read_lock() used illegally while idle!
> [12140.220507] 
> [12140.220507] other info that might help us debug this:
> [12140.220507] 
> [12140.220507] 
> [12140.220507] RCU used illegally from idle CPU!
> [12140.220507] rcu_scheduler_active = 1, debug_locks = 1
> [12140.220507] RCU used illegally from extended quiescent state!
> [12140.220507] 4 locks held by swapper/1/0:
> [12140.253991]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.253991]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.253991]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.253991]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810f3c80>] select_task_rq_fair+0xb0/0x5c0
> [12140.253991] 
> [12140.253991] stack backtrace:
> [12140.253991] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.253991] Call Trace:
> [12140.253991]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.253991]  [<ffffffff810f3ce5>] select_task_rq_fair+0x115/0x5c0
> [12140.253991]  [<ffffffff810f3c80>] ? select_task_rq_fair+0xb0/0x5c0
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec561>] try_to_wake_up+0x191/0x290
> [12140.253991]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.253991]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.253991]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.253991]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.253991]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.253991]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.253991]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.253991]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.253991]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.253991]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.253991]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.253991]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.253991]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.253991]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.253991]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.253991]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> [12140.253991] 
> [12140.253991] ===============================
> [12140.253991] [ INFO: suspicious RCU usage. ]
> [12140.253991] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.253991] -------------------------------
> [12140.253991] kernel/sched/fair.c:2716 suspicious rcu_dereference_check() usage!
> [12140.253991] 
> [12140.253991] other info that might help us debug this:
> [12140.253991] 
> [12140.253991] 
> [12140.253991] RCU used illegally from idle CPU!
> [12140.253991] rcu_scheduler_active = 1, debug_locks = 1
> [12140.253991] RCU used illegally from extended quiescent state!
> [12140.253991] 4 locks held by swapper/1/0:
> [12140.253991]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.253991]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.253991]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.253991]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810f3c80>] select_task_rq_fair+0xb0/0x5c0
> [12140.253991] 
> [12140.253991] stack backtrace:
> [12140.253991] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.253991] Call Trace:
> [12140.253991]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.253991]  [<ffffffff810f3d4c>] select_task_rq_fair+0x17c/0x5c0
> [12140.253991]  [<ffffffff810f3c80>] ? select_task_rq_fair+0xb0/0x5c0
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec561>] try_to_wake_up+0x191/0x290
> [12140.253991]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.253991]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.253991]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.253991]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.253991]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.253991]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.253991]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.253991]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.253991]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.253991]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.253991]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.253991]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.253991]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.253991]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.253991]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.253991]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> [12140.253991] 
> [12140.253991] ===============================
> [12140.253991] [ INFO: suspicious RCU usage. ]
> [12140.253991] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.253991] -------------------------------
> [12140.253991] kernel/sched/fair.c:2660 suspicious rcu_dereference_check() usage!
> [12140.253991] 
> [12140.253991] other info that might help us debug this:
> [12140.253991] 
> [12140.253991] 
> [12140.253991] RCU used illegally from idle CPU!
> [12140.253991] rcu_scheduler_active = 1, debug_locks = 1
> [12140.253991] RCU used illegally from extended quiescent state!
> [12140.253991] 4 locks held by swapper/1/0:
> [12140.253991]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.253991]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.253991]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.253991]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810f3c80>] select_task_rq_fair+0xb0/0x5c0
> [12140.253991] 
> [12140.253991] stack backtrace:
> [12140.253991] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.253991] Call Trace:
> [12140.253991]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.253991]  [<ffffffff810f062f>] select_idle_sibling+0xaf/0x1c0
> [12140.253991]  [<ffffffff810f3f51>] select_task_rq_fair+0x381/0x5c0
> [12140.253991]  [<ffffffff810f3c80>] ? select_task_rq_fair+0xb0/0x5c0
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec561>] try_to_wake_up+0x191/0x290
> [12140.253991]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.253991]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.253991]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.253991]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.253991]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.253991]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.253991]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.253991]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.253991]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.253991]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.253991]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.253991]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.253991]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.253991]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.253991]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.253991]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> [12140.253991] 
> [12140.253991] ===============================
> [12140.253991] [ INFO: suspicious RCU usage. ]
> [12140.253991] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.253991] -------------------------------
> [12140.253991] include/linux/rcupdate.h:750 rcu_read_unlock() used illegally while idle!
> [12140.253991] 
> [12140.253991] other info that might help us debug this:
> [12140.253991] 
> [12140.253991] 
> [12140.253991] RCU used illegally from idle CPU!
> [12140.253991] rcu_scheduler_active = 1, debug_locks = 1
> [12140.253991] RCU used illegally from extended quiescent state!
> [12140.253991] 4 locks held by swapper/1/0:
> [12140.253991]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.253991]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.253991]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.253991]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810f3c80>] select_task_rq_fair+0xb0/0x5c0
> [12140.253991] 
> [12140.253991] stack backtrace:
> [12140.253991] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.253991] Call Trace:
> [12140.253991]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.253991]  [<ffffffff810f412a>] select_task_rq_fair+0x55a/0x5c0
> [12140.253991]  [<ffffffff810f3c80>] ? select_task_rq_fair+0xb0/0x5c0
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.253991]  [<ffffffff810ec561>] try_to_wake_up+0x191/0x290
> [12140.253991]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.253991]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.253991]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.253991]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.253991]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.253991]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.253991]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.253991]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.253991]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.253991]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.253991]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.253991]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.253991]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.253991]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.253991]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.253991]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> [12140.623131] 
> [12140.623131] ===============================
> [12140.623131] [ INFO: suspicious RCU usage. ]
> [12140.623131] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.623131] -------------------------------
> [12140.623131] include/linux/rcupdate.h:729 rcu_read_lock() used illegally while idle!
> [12140.623131] 
> [12140.623131] other info that might help us debug this:
> [12140.623131] 
> [12140.623131] 
> [12140.623131] RCU used illegally from idle CPU!
> [12140.623131] rcu_scheduler_active = 1, debug_locks = 1
> [12140.623131] RCU used illegally from extended quiescent state!
> [12140.623131] 4 locks held by swapper/1/0:
> [12140.623131]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.623131]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.623131]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.623131]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810ea4c0>] ttwu_stat+0x50/0x230
> [12140.623131] 
> [12140.623131] stack backtrace:
> [12140.623131] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.623131] Call Trace:
> [12140.623131]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.623131]  [<ffffffff810ea537>] ttwu_stat+0xc7/0x230
> [12140.623131]  [<ffffffff810ea4c0>] ? ttwu_stat+0x50/0x230
> [12140.623131]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.623131]  [<ffffffff810ec62a>] try_to_wake_up+0x25a/0x290
> [12140.623131]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.623131]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.623131]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.623131]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.623131]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.623131]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.623131]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.623131]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.623131]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.623131]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.623131]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.623131]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.623131]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.623131]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.623131]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.623131]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> [12140.623131] 
> [12140.623131] ===============================
> [12140.623131] [ INFO: suspicious RCU usage. ]
> [12140.623131] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.623131] -------------------------------
> [12140.623131] kernel/sched/core.c:1375 suspicious rcu_dereference_check() usage!
> [12140.623131] 
> [12140.623131] other info that might help us debug this:
> [12140.623131] 
> [12140.623131] 
> [12140.623131] RCU used illegally from idle CPU!
> [12140.623131] rcu_scheduler_active = 1, debug_locks = 1
> [12140.623131] RCU used illegally from extended quiescent state!
> [12140.623131] 4 locks held by swapper/1/0:
> [12140.623131]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.623131]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.623131]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.623131]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810ea4c0>] ttwu_stat+0x50/0x230
> [12140.623131] 
> [12140.623131] stack backtrace:
> [12140.623131] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.623131] Call Trace:
> [12140.623131]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.623131]  [<ffffffff810ea5a8>] ttwu_stat+0x138/0x230
> [12140.623131]  [<ffffffff810ea4c0>] ? ttwu_stat+0x50/0x230
> [12140.623131]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.623131]  [<ffffffff810ec62a>] try_to_wake_up+0x25a/0x290
> [12140.623131]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.623131]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.623131]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.623131]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.623131]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.623131]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.623131]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.623131]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.623131]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.623131]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.623131]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.623131]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.623131]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.623131]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.623131]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.623131]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> [12140.623131] 
> [12140.623131] ===============================
> [12140.623131] [ INFO: suspicious RCU usage. ]
> [12140.623131] 3.4.0-rc1-next-20120402-sasha #46 Tainted: G        W   
> [12140.623131] -------------------------------
> [12140.623131] include/linux/rcupdate.h:750 rcu_read_unlock() used illegally while idle!
> [12140.623131] 
> [12140.623131] other info that might help us debug this:
> [12140.623131] 
> [12140.623131] 
> [12140.623131] RCU used illegally from idle CPU!
> [12140.623131] rcu_scheduler_active = 1, debug_locks = 1
> [12140.623131] RCU used illegally from extended quiescent state!
> [12140.623131] 4 locks held by swapper/1/0:
> [12140.623131]  #0:  (&(&async_pf_sleepers[i].lock)->rlock){..-...}, at: [<ffffffff8107cdc8>] kvm_async_pf_task_wake+0x48/0x130
> [12140.623131]  #1:  (&n.wq){......}, at: [<ffffffff810e200d>] __wake_up+0x2d/0x70
> [12140.623131]  #2:  (&p->pi_lock){-.-.-.}, at: [<ffffffff810ec404>] try_to_wake_up+0x34/0x290
> [12140.623131]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff810ea4c0>] ttwu_stat+0x50/0x230
> [12140.623131] 
> [12140.623131] stack backtrace:
> [12140.623131] Pid: 0, comm: swapper/1 Tainted: G        W    3.4.0-rc1-next-20120402-sasha #46
> [12140.623131] Call Trace:
> [12140.623131]  [<ffffffff81114173>] lockdep_rcu_suspicious+0x113/0x130
> [12140.623131]  [<ffffffff810ea643>] ttwu_stat+0x1d3/0x230
> [12140.623131]  [<ffffffff810ea4c0>] ? ttwu_stat+0x50/0x230
> [12140.623131]  [<ffffffff810ec404>] ? try_to_wake_up+0x34/0x290
> [12140.623131]  [<ffffffff810ec62a>] try_to_wake_up+0x25a/0x290
> [12140.623131]  [<ffffffff81114850>] ? __lock_acquired+0x1c0/0x210
> [12140.623131]  [<ffffffff810ec66d>] default_wake_function+0xd/0x10
> [12140.623131]  [<ffffffff810d7208>] autoremove_wake_function+0x18/0x40
> [12140.623131]  [<ffffffff810e11e2>] __wake_up_common+0x52/0x90
> [12140.623131]  [<ffffffff810e200d>] ? __wake_up+0x2d/0x70
> [12140.623131]  [<ffffffff810e2023>] __wake_up+0x43/0x70
> [12140.623131]  [<ffffffff8107cb07>] apf_task_wake_one+0x87/0x90
> [12140.623131]  [<ffffffff8107cdf5>] kvm_async_pf_task_wake+0x75/0x130
> [12140.623131]  [<ffffffff8107d1e6>] do_async_page_fault+0x86/0xa0
> [12140.623131]  [<ffffffff82657a55>] async_page_fault+0x25/0x30
> [12140.623131]  [<ffffffff8107d626>] ? native_safe_halt+0x6/0x10
> [12140.623131]  [<ffffffff81116fed>] ? trace_hardirqs_on+0xd/0x10
> [12140.623131]  [<ffffffff8105857d>] default_idle+0x4d/0xa0
> [12140.623131]  [<ffffffff810582af>] cpu_idle+0x11f/0x180
> [12140.623131]  [<ffffffff8264b9e0>] ? setup_APIC_timer+0x88/0x8c
> [12140.623131]  [<ffffffff8264b004>] start_secondary+0xe1/0xe8
> 
> -- 
> 
> Sasha.
> 

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