[NETPOLL]: fix initialization/NAPI race

This fixes a race during initialization with the NAPI softirq
processing by using an RCU approach.

This race was discovered when refill_skbs() was added to
the setup code.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 4 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 52a3bf7ae177..faf59b02c4bf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1696,7 +1696,8 @@ static void net_rx_action(struct softirq_action *h)
         struct softnet_data *queue = &__get_cpu_var(softnet_data);
         unsigned long start_time = jiffies;
         int budget = netdev_budget;
-        
+        void *have;
+
         local_irq_disable();
 
         while (!list_empty(&queue->poll_list)) {
@@ -1709,10 +1710,10 @@ static void net_rx_action(struct softirq_action *h)
 
                 dev = list_entry(queue->poll_list.next,
                                  struct net_device, poll_list);
-                netpoll_poll_lock(dev);
+                have = netpoll_poll_lock(dev);
 
                 if (dev->quota <= 0 || dev->poll(dev, &budget)) {
-                        netpoll_poll_unlock(dev);
+                        netpoll_poll_unlock(have);
                         local_irq_disable();
                         list_del(&dev->poll_list);
                         list_add_tail(&dev->poll_list, &queue->poll_list);
@@ -1721,7 +1722,7 @@ static void net_rx_action(struct softirq_action *h)
                         else
                                 dev->quota = dev->weight;
                 } else {
-                        netpoll_poll_unlock(dev);
+                        netpoll_poll_unlock(have);
                         dev_put(dev);
                         local_irq_disable();
                 }
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index c02a08da6d42..996787bca17f 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -732,6 +732,9 @@ int netpoll_setup(struct netpoll *np)
         /* last thing to do is link it to the net device structure */
         ndev->npinfo = npinfo;
 
+        /* avoid racing with NAPI reading npinfo */
+        synchronize_rcu();
+
         return 0;
 
  release: