From e5c239cfd5b0ec22751c099dbf4d91f3c504a64f Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Thu, 8 May 2008 19:47:01 -0300 Subject: [PATCH] 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 Signed-off-by: Avi Kivity --- virt/kvm/kvm_main.c | 29 +++++++++++++++-------------- 1 file changed, 15 insertions(+), 14 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index f7ba099049..2d29e260da 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -758,25 +758,26 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn) */ void kvm_vcpu_block(struct kvm_vcpu *vcpu) { - DECLARE_WAITQUEUE(wait, current); - - add_wait_queue(&vcpu->wq, &wait); - - /* - * 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); + DEFINE_WAIT(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; + 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) -- 2.39.5