net: fix problem in dequeuing from input_pkt_queue

Fix some issues introduced in batch skb dequeuing for input_pkt_queue.
The primary issue it that the queue head must be incremented only
after a packet has been processed, that is only after
__netif_receive_skb has been called.  This is needed for the mechanism
to prevent OOO packet in RFS.  Also when flushing the input_pkt_queue
and process_queue, the process queue should be done first to prevent
OOO packets.

Because the input_pkt_queue has been effectively split into two queues,
the calculation of the tail ptr is no longer correct.  The correct value
would be head+input_pkt_queue->len+process_queue->len.  To avoid
this calculation we added an explict input_queue_tail in softnet_data.
The tail value is simply incremented when queuing to input_pkt_queue.

Signed-off-by: Tom Herbert <therbert@google.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a1bff65..2564195 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1407,17 +1407,25 @@ struct softnet_data {
        struct softnet_data     *rps_ipi_next;
        unsigned int            cpu;
        unsigned int            input_queue_head;
+       unsigned int            input_queue_tail;
 #endif
        unsigned                dropped;
        struct sk_buff_head     input_pkt_queue;
        struct napi_struct      backlog;
 };
 
-static inline void input_queue_head_add(struct softnet_data *sd,
-                                       unsigned int len)
+static inline void input_queue_head_incr(struct softnet_data *sd)
 {
 #ifdef CONFIG_RPS
-       sd->input_queue_head += len;
+       sd->input_queue_head++;
+#endif
+}
+
+static inline void input_queue_tail_incr_save(struct softnet_data *sd,
+                                             unsigned int *qtail)
+{
+#ifdef CONFIG_RPS
+       *qtail = ++sd->input_queue_tail;
 #endif
 }
 

diff --git a/net/core/dev.c b/net/core/dev.c
index 6c82065..0aab66d 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2426,10 +2426,7 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
                if (skb_queue_len(&sd->input_pkt_queue)) {
 enqueue:
                        __skb_queue_tail(&sd->input_pkt_queue, skb);
-#ifdef CONFIG_RPS
-                       *qtail = sd->input_queue_head +
-                                       skb_queue_len(&sd->input_pkt_queue);
-#endif
+                       input_queue_tail_incr_save(sd, qtail);
                        rps_unlock(sd);
                        local_irq_restore(flags);
                        return NET_RX_SUCCESS;
@@ -2964,7 +2961,7 @@ static void flush_backlog(void *arg)
                if (skb->dev == dev) {
                        __skb_unlink(skb, &sd->input_pkt_queue);
                        kfree_skb(skb);
-                       input_queue_head_add(sd, 1);
+                       input_queue_head_incr(sd);
                }
        }
        rps_unlock(sd);
@@ -2973,6 +2970,7 @@ static void flush_backlog(void *arg)
                if (skb->dev == dev) {
                        __skb_unlink(skb, &sd->process_queue);
                        kfree_skb(skb);
+                       input_queue_head_incr(sd);
                }
        }
 }
@@ -3328,18 +3326,20 @@ static int process_backlog(struct napi_struct *napi, int quota)
                while ((skb = __skb_dequeue(&sd->process_queue))) {
                        local_irq_enable();
                        __netif_receive_skb(skb);
-                       if (++work >= quota)
-                               return work;
                        local_irq_disable();
+                       input_queue_head_incr(sd);
+                       if (++work >= quota) {
+                               local_irq_enable();
+                               return work;
+                       }
                }
 
                rps_lock(sd);
                qlen = skb_queue_len(&sd->input_pkt_queue);
-               if (qlen) {
-                       input_queue_head_add(sd, qlen);
+               if (qlen)
                        skb_queue_splice_tail_init(&sd->input_pkt_queue,
                                                   &sd->process_queue);
-               }
+
                if (qlen < quota - work) {
                        /*
                         * Inline a custom version of __napi_complete().
@@ -5679,12 +5679,14 @@ static int dev_cpu_callback(struct notifier_block *nfb,
        local_irq_enable();
 
        /* Process offline CPU's input_pkt_queue */
-       while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
+       while ((skb = __skb_dequeue(&oldsd->process_queue))) {
                netif_rx(skb);
-               input_queue_head_add(oldsd, 1);
+               input_queue_head_incr(oldsd);
        }
-       while ((skb = __skb_dequeue(&oldsd->process_queue)))
+       while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
                netif_rx(skb);
+               input_queue_head_incr(oldsd);
+       }
 
        return NOTIFY_OK;
 }