kvm: Serialize wq active checks in kvm_vcpu_wake_up()

This is a generic call and can be suceptible to races
in reading the wq task_list while another task is adding
itself to the list. Add a full barrier by using the
swq_has_sleeper() helper.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2d7df5cc955bfb7c4120734bb642bf0af3a6a198..9deb5a245b83032ffaa960d42cd6f01ecb614b1b 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2187,7 +2187,7 @@ bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
        struct swait_queue_head *wqp;
 
        wqp = kvm_arch_vcpu_wq(vcpu);
-       if (swait_active(wqp)) {
+       if (swq_has_sleeper(wqp)) {
                swake_up(wqp);
                ++vcpu->stat.halt_wakeup;
                return true;