This patch checks the new event idx to make sure used event idx never
goes back. This is used to synchronize the calls between
virtqueue_enable_cb_delayed() and virtqueue_enable_cb().
Cc: Rusty Russell <ru...@rustcorp.com.au>
Cc: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Jason Wang <jasow...@redhat.com>
---
drivers/virtio/virtio_ring.c | 7 +++++--
1 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 3b1f89b..1b3929f 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -559,14 +559,17 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue
*_vq)
u16 last_used_idx;
START_USE(vq);
-
+ last_used_idx = vq->last_used_idx;
/* We optimistically turn back on interrupts, then check if there was
* more to do. */
/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
* either clear the flags bit or point the event index at the next
* entry. Always do both to keep code simple. */
vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
- vring_used_event(&vq->vring) = last_used_idx = vq->last_used_idx;
+ /* Make sure used event never go backwards */
+ if (!vring_need_event(vring_used_event(&vq->vring),
+ vq->vring.avail->idx, last_used_idx))
+ vring_used_event(&vq->vring) = last_used_idx;
END_USE(vq);
return last_used_idx;
}
--
1.7.1
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