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KVM: Fix kvm_vcpu_block() task state race

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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>
This commit is contained in:
Marcelo Tosatti 2008-05-08 19:47:01 -03:00 • committed by Avi Kivity
parent bd25ed033a
commit e5c239cfd5
1 changed files with 13 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

25
virt/kvm/kvm_main.c
View file

@ -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);
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);
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)