net: netif_rx() must disable preemption

Eric Paris reported netif_rx() is calling smp_processor_id() from
preemptible context, in particular when caller is
ip_dev_loopback_xmit().

RPS commit added this smp_processor_id() call, this patch makes sure
preemption is disabled. rps_get_cpus() wants rcu_read_lock() anyway, we
can dot it a bit earlier.

Reported-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 876b1112d5bafd28038d31810ba53bd4adcec9bb..e8041eb76ac1935adbe35d034fa9d8f9d45a53be 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2206,6 +2206,7 @@ DEFINE_PER_CPU(struct netif_rx_stats, netdev_rx_stat) = { 0, };
 /*
  * get_rps_cpu is called from netif_receive_skb and returns the target
  * CPU from the RPS map of the receiving queue for a given skb.
+ * rcu_read_lock must be held on entry.
  */
 static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb)
 {
@@ -2217,8 +2218,6 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb)
        u8 ip_proto;
        u32 addr1, addr2, ports, ihl;
 
-       rcu_read_lock();
-
        if (skb_rx_queue_recorded(skb)) {
                u16 index = skb_get_rx_queue(skb);
                if (unlikely(index >= dev->num_rx_queues)) {
@@ -2296,7 +2295,6 @@ got_hash:
        }
 
 done:
-       rcu_read_unlock();
        return cpu;
 }
 
@@ -2392,7 +2390,7 @@ enqueue:
 
 int netif_rx(struct sk_buff *skb)
 {
-       int cpu;
+       int ret;
 
        /* if netpoll wants it, pretend we never saw it */
        if (netpoll_rx(skb))
@@ -2402,14 +2400,21 @@ int netif_rx(struct sk_buff *skb)
                net_timestamp(skb);
 
 #ifdef CONFIG_RPS
-       cpu = get_rps_cpu(skb->dev, skb);
-       if (cpu < 0)
-               cpu = smp_processor_id();
+       {
+               int cpu;
+
+               rcu_read_lock();
+               cpu = get_rps_cpu(skb->dev, skb);
+               if (cpu < 0)
+                       cpu = smp_processor_id();
+               ret = enqueue_to_backlog(skb, cpu);
+               rcu_read_unlock();
+       }
 #else
-       cpu = smp_processor_id();
+       ret = enqueue_to_backlog(skb, get_cpu());
+       put_cpu();
 #endif
-
-       return enqueue_to_backlog(skb, cpu);
+       return ret;
 }
 EXPORT_SYMBOL(netif_rx);