[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>

1 files changed, 13 insertions, 6 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