[NET]: Can use __get_cpu_var() instead of per_cpu() in loopback driver.

As BHs are off in loopback_xmit(), preemption cannot occurs, so we can
use __get_cpu_var() instead of per_cpu() (and avoid a
preempt_enable()/preempt_disable() pair)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/loopback.c

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 93fbea1..82c10de 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -153,14 +153,14 @@
 #endif
 	dev->last_rx = jiffies;
 
-	lb_stats = &per_cpu(pcpu_lstats, get_cpu());
+	/* it's OK to use __get_cpu_var() because BHs are off */
+	lb_stats = &__get_cpu_var(pcpu_lstats);
 	lb_stats->bytes += skb->len;
 	lb_stats->packets++;
-	put_cpu();
 
 	netif_rx(skb);
 
-	return(0);
+	return 0;
 }
 
 static struct net_device_stats loopback_stats;