kvm,mips: Fix potential swait_active() races
authorDavidlohr Bueso <dave@stgolabs.net>
Wed, 13 Sep 2017 20:08:24 +0000 (13:08 -0700)
committerPaolo Bonzini <pbonzini@redhat.com>
Fri, 15 Sep 2017 14:57:13 +0000 (16:57 +0200)
For example, the following could occur, making us miss a wakeup:

CPU0 CPU1
kvm_vcpu_block kvm_mips_comparecount_func
  [L] swait_active(&vcpu->wq)
  [S] prepare_to_swait(&vcpu->wq)
  [L] if (!kvm_vcpu_has_pending_timer(vcpu))
         schedule()                       [S] queue_timer_int(vcpu)

Ensure that the swait_active() check is not hoisted over the interrupt.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
arch/mips/kvm/mips.c

index bce2a6431430366ee626ddc4f6282665caeb7f06..d535edc01434117a8809fc21fb152226e0b46521 100644 (file)
@@ -514,7 +514,7 @@ int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu,
 
        dvcpu->arch.wait = 0;
 
-       if (swait_active(&dvcpu->wq))
+       if (swq_has_sleeper(&dvcpu->wq))
                swake_up(&dvcpu->wq);
 
        return 0;
@@ -1179,7 +1179,7 @@ static void kvm_mips_comparecount_func(unsigned long data)
        kvm_mips_callbacks->queue_timer_int(vcpu);
 
        vcpu->arch.wait = 0;
-       if (swait_active(&vcpu->wq))
+       if (swq_has_sleeper(&vcpu->wq))
                swake_up(&vcpu->wq);
 }