[PATCH net-next-2.6] net: introduce rcu_dereference_read_lock_or_rtnl

[Eric Dumazet <eric.dumazet@gmail.com>]

We use rcu_dereference_check(p, rcu_read_lock_held() ||
lockdep_rtnl_is_held()) several times in network stack.

More usages to come too, so its time to create a helper.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
include/linux/rtnetlink.h |   12 ++++++++++++

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 58d4449..5ba48bb 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -745,10 +745,22 @@ extern void rtnl_lock(void);
 extern void rtnl_unlock(void);
 extern int rtnl_trylock(void);
 extern int rtnl_is_locked(void);
+
 #ifdef CONFIG_PROVE_LOCKING
 extern int lockdep_rtnl_is_held(void);
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 
+/**
+ * rcu_dereference_read_lock_or_rtnl - rcu_dereference with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * Do an rcu_dereference(p), but check caller either holds rcu_read_lock()
+ * or RTNL
+ */
+#define rcu_dereference_read_lock_or_rtnl(p)				\
+		rcu_dereference_check(p, rcu_read_lock_held() ||	\
+					 lockdep_rtnl_is_held());
+
 extern void rtnetlink_init(void);
 extern void __rtnl_unlock(void);