xen-netback: Fix Rx stall due to race condition
The recent patch to fix receive side flow control
(11b57f90257c1d6a91cee720151b69e0c2020cf6: xen-netback: stop vif thread
spinning if frontend is unresponsive) solved the spinning thread problem,
however caused an another one. The receive side can stall, if:
- [THREAD] xenvif_rx_action sets rx_queue_stopped to true
- [INTERRUPT] interrupt happens, and sets rx_event to true
- [THREAD] then xenvif_kthread sets rx_event to false
- [THREAD] rx_work_todo doesn't return true anymore
Also, if interrupt sent but there is still no room in the ring, it take quite a
long time until xenvif_rx_action realize it. This patch ditch that two variable,
and rework rx_work_todo. If the thread finds it can't fit more skb's into the
ring, it saves the last slot estimation into rx_last_skb_slots, otherwise it's
kept as 0. Then rx_work_todo will check if:
- there is something to send to the ring (like before)
- there is space for the topmost packet in the queue
I think that's more natural and optimal thing to test than two bool which are
set somewhere else.
Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 6b62c3e..e5284bc 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -476,7 +476,6 @@
unsigned long offset;
struct skb_cb_overlay *sco;
bool need_to_notify = false;
- bool ring_full = false;
struct netrx_pending_operations npo = {
.copy = vif->grant_copy_op,
@@ -486,7 +485,7 @@
skb_queue_head_init(&rxq);
while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
- int max_slots_needed;
+ RING_IDX max_slots_needed;
int i;
/* We need a cheap worse case estimate for the number of
@@ -509,9 +508,10 @@
if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
skb_queue_head(&vif->rx_queue, skb);
need_to_notify = true;
- ring_full = true;
+ vif->rx_last_skb_slots = max_slots_needed;
break;
- }
+ } else
+ vif->rx_last_skb_slots = 0;
sco = (struct skb_cb_overlay *)skb->cb;
sco->meta_slots_used = xenvif_gop_skb(skb, &npo);
@@ -522,8 +522,6 @@
BUG_ON(npo.meta_prod > ARRAY_SIZE(vif->meta));
- vif->rx_queue_stopped = !npo.copy_prod && ring_full;
-
if (!npo.copy_prod)
goto done;
@@ -1473,8 +1471,8 @@
static inline int rx_work_todo(struct xenvif *vif)
{
- return (!skb_queue_empty(&vif->rx_queue) && !vif->rx_queue_stopped) ||
- vif->rx_event;
+ return !skb_queue_empty(&vif->rx_queue) &&
+ xenvif_rx_ring_slots_available(vif, vif->rx_last_skb_slots);
}
static inline int tx_work_todo(struct xenvif *vif)
@@ -1560,8 +1558,6 @@
if (!skb_queue_empty(&vif->rx_queue))
xenvif_rx_action(vif);
- vif->rx_event = false;
-
if (skb_queue_empty(&vif->rx_queue) &&
netif_queue_stopped(vif->dev))
xenvif_start_queue(vif);