vhost: handle wrap around in # of bufs math
The meth for calculating the # of outstanding buffers gives
incorrect results when vq->upend_idx wraps around zero.
Fix that.
Signed-off-by: Shirley Ma <xma@us.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 248b250..882a51f 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -182,15 +182,21 @@
break;
/* Nothing new? Wait for eventfd to tell us they refilled. */
if (head == vq->num) {
+ int num_pends;
+
wmem = atomic_read(&sock->sk->sk_wmem_alloc);
if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
tx_poll_start(net, sock);
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
- /* If more outstanding DMAs, queue the work */
- if (unlikely(vq->upend_idx - vq->done_idx >
- VHOST_MAX_PEND)) {
+ /* If more outstanding DMAs, queue the work.
+ * Handle upend_idx wrap around
+ */
+ num_pends = likely(vq->upend_idx >= vq->done_idx) ?
+ (vq->upend_idx - vq->done_idx) :
+ (vq->upend_idx + UIO_MAXIOV - vq->done_idx);
+ if (unlikely(num_pends > VHOST_MAX_PEND)) {
tx_poll_start(net, sock);
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;