Web lists-archives.com

[PATCH 7/7] kvm,mips: Fix potential swait_active() races




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@xxxxxxx>
---
 arch/mips/kvm/mips.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index bce2a6431430..d535edc01434 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -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);
 }
 
-- 
2.12.0