2016-02-03 17:23+0100, Radim Krčmář: > A misuse of atomic operations opened a window > > kvm_pit_ack_irq: | pit_timer_fn: > value = atomic_dec_return(&ps->pending); | > | !atomic_read(&ps->pending) > if (value < 0) atomic_inc(&ps->pending); | > > If ps->pending starts as 0 and we are using the discard policy, we don't > inject any interrupt in kvm_pit_ack_irq or pit_timer_fn, leading to a > missed PIT cycle. > > Signed-off-by: Radim Krčmář <[email protected]> > --- > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c > @@ -239,13 +239,7 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier > *kian) > int value; > > spin_lock(&ps->inject_lock); > - value = atomic_dec_return(&ps->pending); > - if (value < 0) > - /* spurious acks can be generated if, for example, the > - * PIC is being reset. Handle it gracefully here > - */ > - atomic_inc(&ps->pending); > - else if (value > 0) > + if (atomic_add_unless(&ps->pending, -1, 0))
This is not right, I'll redo the series. Sorry.
