KVM: Fix kvm_vcpu_block() task state race
There's still a race in kvm_vcpu_block(), if a wake_up_interruptible()
call happens before the task state is set to TASK_INTERRUPTIBLE:
CPU0 CPU1
kvm_vcpu_block
add_wait_queue
kvm_cpu_has_interrupt = 0
set interrupt
if (waitqueue_active())
wake_up_interruptible()
kvm_cpu_has_pending_timer
kvm_arch_vcpu_runnable
signal_pending
set_current_state(TASK_INTERRUPTIBLE)
schedule()
Can be fixed by using prepare_to_wait() which sets the task state before
testing for the wait condition.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f7ba099..2d29e26 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -758,25 +758,26 @@
*/
void kvm_vcpu_block(struct kvm_vcpu *vcpu)
{
- DECLARE_WAITQUEUE(wait, current);
+ DEFINE_WAIT(wait);
- add_wait_queue(&vcpu->wq, &wait);
+ for (;;) {
+ prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
- /*
- * We will block until either an interrupt or a signal wakes us up
- */
- while (!kvm_cpu_has_interrupt(vcpu)
- && !kvm_cpu_has_pending_timer(vcpu)
- && !signal_pending(current)
- && !kvm_arch_vcpu_runnable(vcpu)) {
- set_current_state(TASK_INTERRUPTIBLE);
+ if (kvm_cpu_has_interrupt(vcpu))
+ break;
+ if (kvm_cpu_has_pending_timer(vcpu))
+ break;
+ if (kvm_arch_vcpu_runnable(vcpu))
+ break;
+ if (signal_pending(current))
+ break;
+
vcpu_put(vcpu);
schedule();
vcpu_load(vcpu);
}
- __set_current_state(TASK_RUNNING);
- remove_wait_queue(&vcpu->wq, &wait);
+ finish_wait(&vcpu->wq, &wait);
}
void kvm_resched(struct kvm_vcpu *vcpu)