From 81a8deab1ce3816c6a89e3429e234e7d3686da94 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Mon, 4 Feb 2008 23:50:04 -0500 Subject: [PATCH] virtio: handle interrupts after callbacks turned off Anthony Liguori found double interrupt suppression in the virtio_net driver, triggered by two skb_recv_done's in a row. This is because virtio_ring's interrupt suppression is a best-effort optimization: it contains no synchronization so the host can miss it and still send interrupts. But it's certainly nicer for virtio users if calling disable_cb actually disables callbacks, so we check for the race in the interrupt routine. Note: SMP guests might require syncronization here, but since disable_cb is actually called from interrupt context, there has to be some form of synchronization before the next same interrupt handler is called (Linux guarantees that the same device's irq handler will never run simultanously on multiple CPUs). Signed-off-by: Rusty Russell --- drivers/virtio/virtio_ring.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 9849babd6b..9859213aa6 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -255,6 +255,13 @@ irqreturn_t vring_interrupt(int irq, void *_vq) if (unlikely(vq->broken)) return IRQ_HANDLED; + /* Other side may have missed us turning off the interrupt, + * but we should preserve disable semantic for virtio users. */ + if (unlikely(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) { + pr_debug("virtqueue interrupt after disable for %p\n", vq); + return IRQ_HANDLED; + } + pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); if (vq->vq.callback) vq->vq.callback(&vq->vq); -- 2.39.5