datapath: Replace rcu_dereference() with rcu_access_pointer()

The "rcu_dereference()" call is used directly in a condition.
Since its return value is never dereferenced it is recommended to use
"rcu_access_pointer()" instead of "rcu_dereference()".
Therefore, this patch makes the replacement.

The following Coccinelle semantic patch was used:
@@
@@

(
 if(
 (<+...
- rcu_dereference
+ rcu_access_pointer
  (...)
  ...+>)) {...}
|
 while(
 (<+...
- rcu_dereference
+ rcu_access_pointer
  (...)
  ...+>)) {...}
)

Signed-off-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Pravin B Shelar <pshelar@nicira.com>

datapath/flow.c

@@ -93,7 +93,7 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16 tcp_flags,
 			 * allocated stats as we have already locked them.
 			 */
 			if (likely(flow->stats_last_writer != NUMA_NO_NODE)
-			    && likely(!rcu_dereference(flow->stats[node]))) {
+			    && likely(!rcu_access_pointer(flow->stats[node]))) {
 				/* Try to allocate node-specific stats. */
 				struct flow_stats *new_stats;
 

datapath/linux/compat/include/linux/rcupdate.h

@@ -15,6 +15,10 @@
 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1)
 #endif
 
+#ifndef rcu_access_pointer
+#define rcu_access_pointer(p)	rcu_dereference(p)
+#endif
+
 #ifndef HAVE_RCU_READ_LOCK_HELD
 static inline int rcu_read_lock_held(void)
 {