Commit a0cff57b authored Sep 13, 2017 by Davidlohr Bueso Committed by Paolo Bonzini Sep 15, 2017

kvm,x86: Fix apf_task_wake_one() wq serialization



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>

parent cc1b4680

arch/x86/kernel/kvm.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}

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