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kvm,x86: Fix apf_task_wake_one() wq serialization

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During code inspection, the following potential race was seen:

CPU0   	    		    	     	CPU1
kvm_async_pf_task_wait			apf_task_wake_one
					  [L] swait_active(&n->wq)
  [S] prepare_to_swait(&n.wq)
  [L] if (!hlist_unhahed(&n.link))
	schedule()			  [S] hlist_del_init(&n->link);

Properly serialize swait_active() checks such that a wakeup is
not missed.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Davidlohr Bueso 2017-09-13 13:08:21 -07:00 committed by Paolo Bonzini
parent cc1b46803a
commit a0cff57bb2
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/kvm.c
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@ -180,7 +180,7 @@ static void apf_task_wake_one(struct kvm_task_sleep_node *n)
hlist_del_init(&n->link);
if (n->halted)
smp_send_reschedule(n->cpu);
else if (swait_active(&n->wq))
else if (swq_has_sleeper(&n->wq))
swake_up(&n->wq);
}