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xen-netback: Fix Rx stall due to race condition
The recent patch to fix receive side flow control
(11b57f9025
: 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>
This commit is contained in:
parent
bce3ea81d5
commit
9ab9831b4c
3 changed files with 7 additions and 16 deletions
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@ -143,11 +143,7 @@ struct xenvif {
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char rx_irq_name[IFNAMSIZ+4]; /* DEVNAME-rx */
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struct xen_netif_rx_back_ring rx;
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struct sk_buff_head rx_queue;
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bool rx_queue_stopped;
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/* Set when the RX interrupt is triggered by the frontend.
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* The worker thread may need to wake the queue.
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*/
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bool rx_event;
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RING_IDX rx_last_skb_slots;
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/* This array is allocated seperately as it is large */
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struct gnttab_copy *grant_copy_op;
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@ -100,7 +100,6 @@ static irqreturn_t xenvif_rx_interrupt(int irq, void *dev_id)
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{
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struct xenvif *vif = dev_id;
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vif->rx_event = true;
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xenvif_kick_thread(vif);
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return IRQ_HANDLED;
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@ -476,7 +476,6 @@ static void xenvif_rx_action(struct xenvif *vif)
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unsigned long offset;
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struct skb_cb_overlay *sco;
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bool need_to_notify = false;
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bool ring_full = false;
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struct netrx_pending_operations npo = {
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.copy = vif->grant_copy_op,
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@ -486,7 +485,7 @@ static void xenvif_rx_action(struct xenvif *vif)
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skb_queue_head_init(&rxq);
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while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
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int max_slots_needed;
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RING_IDX max_slots_needed;
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int i;
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/* We need a cheap worse case estimate for the number of
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@ -509,9 +508,10 @@ static void xenvif_rx_action(struct xenvif *vif)
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if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
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skb_queue_head(&vif->rx_queue, skb);
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need_to_notify = true;
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ring_full = true;
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vif->rx_last_skb_slots = max_slots_needed;
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break;
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}
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} else
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vif->rx_last_skb_slots = 0;
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sco = (struct skb_cb_overlay *)skb->cb;
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sco->meta_slots_used = xenvif_gop_skb(skb, &npo);
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@ -522,8 +522,6 @@ static void xenvif_rx_action(struct xenvif *vif)
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BUG_ON(npo.meta_prod > ARRAY_SIZE(vif->meta));
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vif->rx_queue_stopped = !npo.copy_prod && ring_full;
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if (!npo.copy_prod)
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goto done;
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@ -1473,8 +1471,8 @@ static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
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static inline int rx_work_todo(struct xenvif *vif)
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{
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return (!skb_queue_empty(&vif->rx_queue) && !vif->rx_queue_stopped) ||
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vif->rx_event;
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return !skb_queue_empty(&vif->rx_queue) &&
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xenvif_rx_ring_slots_available(vif, vif->rx_last_skb_slots);
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}
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static inline int tx_work_todo(struct xenvif *vif)
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@ -1560,8 +1558,6 @@ int xenvif_kthread(void *data)
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if (!skb_queue_empty(&vif->rx_queue))
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xenvif_rx_action(vif);
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vif->rx_event = false;
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if (skb_queue_empty(&vif->rx_queue) &&
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netif_queue_stopped(vif->dev))
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xenvif_start_queue(vif);
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