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KVM: s390: Fix race condition in kvm_s390_handle_wait 

The call to add_timer was issued before local_int.lock was taken and before
timer_due was set to 0. If the timer expires before the lock is being taken,
the timer function will set timer_due to 1 and exit before the vcpu falls
asleep. Depending on other external events, the vcpu might sleep forever.
This fix pulls setting timer_due to the beginning of the function before
add_timer, which ensures correct behavior.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Carsten Otte 2008-05-21 13:37:44 +02:00 committed by Avi Kivity
parent 1f0d0f094d
commit e52b2af541
1 changed files with 5 additions and 2 deletions
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7
arch/s390/kvm/interrupt.c
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@ -339,6 +339,11 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
if (kvm_cpu_has_interrupt(vcpu))
return 0;
__set_cpu_idle(vcpu);
spin_lock_bh(&vcpu->arch.local_int.lock);
vcpu->arch.local_int.timer_due = 0;
spin_unlock_bh(&vcpu->arch.local_int.lock);
if (psw_interrupts_disabled(vcpu)) {
VCPU_EVENT(vcpu, 3, "%s", "disabled wait");
__unset_cpu_idle(vcpu);
@ -366,8 +371,6 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
no_timer:
spin_lock_bh(&vcpu->arch.local_int.float_int->lock);
spin_lock_bh(&vcpu->arch.local_int.lock);
__set_cpu_idle(vcpu);
vcpu->arch.local_int.timer_due = 0;
add_wait_queue(&vcpu->arch.local_int.wq, &wait);
while (list_empty(&vcpu->arch.local_int.list) &&
list_empty(&vcpu->arch.local_int.float_int->list) &&