This patch disables preemption for a very short time, so it doesn't hurt
preempt-latency. The author of this solution was Peter Zijlstra.

Signed-off-by: John Kacur <jkacur at gmail dot com>
Index: linux-2.6.26.2-rt1-jk/net/core/sock.c
===================================================================
--- linux-2.6.26.2-rt1-jk.orig/net/core/sock.c
+++ linux-2.6.26.2-rt1-jk/net/core/sock.c
@@ -1943,8 +1943,9 @@ static DECLARE_BITMAP(proto_inuse_idx, P
 #ifdef CONFIG_NET_NS
 void sock_prot_inuse_add(struct net *net, struct proto *prot, int val)
 {
-	int cpu = smp_processor_id();
+	int cpu = get_cpu();
 	per_cpu_ptr(net->core.inuse, cpu)->val[prot->inuse_idx] += val;
+	put_cpu();
 }
 EXPORT_SYMBOL_GPL(sock_prot_inuse_add);
 
@@ -1990,7 +1991,9 @@ static DEFINE_PER_CPU(struct prot_inuse,
 
 void sock_prot_inuse_add(struct net *net, struct proto *prot, int val)
 {
-	__get_cpu_var(prot_inuse).val[prot->inuse_idx] += val;
+	int cpu = get_cpu();
+	per_cpu(prot_inuse, cpu).val[prot->inuse_idx] += val;
+	put_cpu();
 }
 EXPORT_SYMBOL_GPL(sock_prot_inuse_add);