linux-kernel - [PATCH] kvm, async_pf: exit idleness when handling KVM_PV_REASON_PAGE_NOT

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Date:	Fri, 19 Oct 2012 12:11:55 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	avi@...hat.com, gleb@...hat.com, mtosatti@...hat.com
Cc:	davej@...hat.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	Sasha Levin <sasha.levin@...cle.com>
Subject: [PATCH] kvm, async_pf: exit idleness when handling KVM_PV_REASON_PAGE_NOT_PRESENT

KVM_PV_REASON_PAGE_NOT_PRESENT kicks cpu out of idleness, but we haven't
marked that spot as an exit from idleness.

Not doing so can cause RCU warnings such as:

[  732.788386] ===============================
[  732.789803] [ INFO: suspicious RCU usage. ]
[  732.790032] 3.7.0-rc1-next-20121019-sasha-00002-g6d8d02d-dirty #63 Tainted: G        W
[  732.790032] -------------------------------
[  732.790032] include/linux/rcupdate.h:738 rcu_read_lock() used illegally while idle!
[  732.790032]
[  732.790032] other info that might help us debug this:
[  732.790032]
[  732.790032]
[  732.790032] RCU used illegally from idle CPU!
[  732.790032] rcu_scheduler_active = 1, debug_locks = 1
[  732.790032] RCU used illegally from extended quiescent state!
[  732.790032] 2 locks held by trinity-child31/8252:
[  732.790032]  #0:  (&rq->lock){-.-.-.}, at: [<ffffffff83a67528>] __schedule+0x178/0x8f0
[  732.790032]  #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff81152bde>] cpuacct_charge+0xe/0x200
[  732.790032]
[  732.790032] stack backtrace:
[  732.790032] Pid: 8252, comm: trinity-child31 Tainted: G        W    3.7.0-rc1-next-20121019-sasha-00002-g6d8d02d-dirty #63
[  732.790032] Call Trace:
[  732.790032]  [<ffffffff8118266b>] lockdep_rcu_suspicious+0x10b/0x120
[  732.790032]  [<ffffffff81152c60>] cpuacct_charge+0x90/0x200
[  732.790032]  [<ffffffff81152bde>] ? cpuacct_charge+0xe/0x200
[  732.790032]  [<ffffffff81158093>] update_curr+0x1a3/0x270
[  732.790032]  [<ffffffff81158a6a>] dequeue_entity+0x2a/0x210
[  732.790032]  [<ffffffff81158ea5>] dequeue_task_fair+0x45/0x130
[  732.790032]  [<ffffffff8114ae29>] dequeue_task+0x89/0xa0
[  732.790032]  [<ffffffff8114bb9e>] deactivate_task+0x1e/0x20
[  732.790032]  [<ffffffff83a67c29>] __schedule+0x879/0x8f0
[  732.790032]  [<ffffffff8117e20d>] ? trace_hardirqs_off+0xd/0x10
[  732.790032]  [<ffffffff810a37a5>] ? kvm_async_pf_task_wait+0x1d5/0x2b0
[  732.790032]  [<ffffffff83a67cf5>] schedule+0x55/0x60
[  732.790032]  [<ffffffff810a37c4>] kvm_async_pf_task_wait+0x1f4/0x2b0
[  732.790032]  [<ffffffff81139e50>] ? abort_exclusive_wait+0xb0/0xb0
[  732.790032]  [<ffffffff81139c25>] ? prepare_to_wait+0x25/0x90
[  732.790032]  [<ffffffff810a3a66>] do_async_page_fault+0x56/0xa0
[  732.790032]  [<ffffffff83a6a6e8>] async_page_fault+0x28/0x30

Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
---
 arch/x86/kernel/kvm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index b3e5e51..4180a87 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -247,7 +247,10 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
 		break;
 	case KVM_PV_REASON_PAGE_NOT_PRESENT:
 		/* page is swapped out by the host. */
+		rcu_irq_enter();
+		exit_idle();
 		kvm_async_pf_task_wait((u32)read_cr2());
+		rcu_irq_exit();
 		break;
 	case KVM_PV_REASON_PAGE_READY:
 		rcu_irq_enter();
-- 
1.7.12.3

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