kvm: free resources after canceling async_pf

When we cancel 'async_pf_execute()', we should behave as if the work was
never scheduled in 'kvm_setup_async_pf()'.
Fixes a bug when we can't unload module because the vm wasn't destroyed.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/async_pf.c

@@ -101,8 +101,11 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
 				   typeof(*work), queue);
 		cancel_work_sync(&work->work);
 		list_del(&work->queue);
-		if (!work->done) /* work was canceled */
+		if (!work->done) { /* work was canceled */
+			mmdrop(work->mm);
+			kvm_put_kvm(vcpu->kvm); /* == work->vcpu->kvm */
 			kmem_cache_free(async_pf_cache, work);
+		}
 	}
 
 	spin_lock(&vcpu->async_pf.lock);