[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>

3 files changed, 21 insertions, 10 deletions

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index be68d94b03d5..5ade54a78dbb 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -9,6 +9,7 @@
 
 #include <linux/netdevice.h>
 #include <linux/interrupt.h>
+#include <linux/rcupdate.h>
 #include <linux/list.h>
 
 struct netpoll;
@@ -61,25 +62,31 @@ static inline int netpoll_rx(struct sk_buff *skb)
         return ret;
 }
 
-static inline void netpoll_poll_lock(struct net_device *dev)
+static inline void *netpoll_poll_lock(struct net_device *dev)
 {
+        rcu_read_lock(); /* deal with race on ->npinfo */
         if (dev->npinfo) {
                 spin_lock(&dev->npinfo->poll_lock);
                 dev->npinfo->poll_owner = smp_processor_id();
+                return dev->npinfo;
         }
+        return NULL;
 }
 
-static inline void netpoll_poll_unlock(struct net_device *dev)
+static inline void netpoll_poll_unlock(void *have)
 {
-        if (dev->npinfo) {
-                dev->npinfo->poll_owner = -1;
-                spin_unlock(&dev->npinfo->poll_lock);
+        struct netpoll_info *npi = have;
+
+        if (npi) {
+                npi->poll_owner = -1;
+                spin_unlock(&npi->poll_lock);
         }
+        rcu_read_unlock();
 }
 
 #else
 #define netpoll_rx(a) 0
-#define netpoll_poll_lock(a)
+#define netpoll_poll_lock(a) 0
 #define netpoll_poll_unlock(a)
 #endif
 
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: