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Commit e5c239cf authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Avi Kivity
Browse files

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: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent bd25ed03

virt/kvm/kvm_main.c

+15 −14
Original line number Original line Diff line number Diff line
@@ -758,25 +758,26 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn) 
 */

 */

void kvm_vcpu_block(struct kvm_vcpu *vcpu)

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);



		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;





	/*

	 * 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);

		vcpu_put(vcpu);

		vcpu_put(vcpu);

		schedule();

		schedule();

		vcpu_load(vcpu);

		vcpu_load(vcpu);

	}

	}





	__set_current_state(TASK_RUNNING);

	finish_wait(&vcpu->wq, &wait);

	remove_wait_queue(&vcpu->wq, &wait);

}

}





void kvm_resched(struct kvm_vcpu *vcpu)

void kvm_resched(struct kvm_vcpu *vcpu)