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 <rkrcmar@xxxxxxxxxx>
---
arch/x86/kvm/i8254.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index b0ea42b78ccd..de5f5018026f 100644
--- 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))
/* in this case, we had multiple outstanding pit interrupts
* that we needed to inject. Reinject
*/
--
2.7.0
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