[RTNETLINK]: Fix bogus ASSERT_RTNL warning

ASSERT_RTNL uses mutex_trylock to test whether the rtnl_mutex is
held. This bogus warnings when running in atomic context, which
f.e. happens when adding secondary unicast addresses through
macvlan or vlan or when synchronizing multicast addresses from
wireless devices.

Mid-term we might want to consider moving all address updates
to process context since the locking seems overly complicated,
for now just fix the bogus warning by changing ASSERT_RTNL to
use mutex_is_locked().

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rtnetlink.h

@@ -740,13 +740,13 @@ extern void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change);
 extern void rtnl_lock(void);
 extern void rtnl_unlock(void);
 extern int rtnl_trylock(void);
+extern int rtnl_is_locked(void);
 
 extern void rtnetlink_init(void);
 extern void __rtnl_unlock(void);
 
 #define ASSERT_RTNL() do { \
-	if (unlikely(rtnl_trylock())) { \
-		rtnl_unlock(); \
+	if (unlikely(!rtnl_is_locked())) { \
 		printk(KERN_ERR "RTNL: assertion failed at %s (%d)\n", \
 		       __FILE__,  __LINE__); \
 		dump_stack(); \

net/core/rtnetlink.c

@@ -82,6 +82,11 @@ int rtnl_trylock(void)
 	return mutex_trylock(&rtnl_mutex);
 }
 
+int rtnl_is_locked(void)
+{
+	return mutex_is_locked(&rtnl_mutex);
+}
+
 static struct rtnl_link *rtnl_msg_handlers[NPROTO];
 
 static inline int rtm_msgindex(int msgtype)
@@ -1402,6 +1407,7 @@ EXPORT_SYMBOL(rtnetlink_put_metrics);
 EXPORT_SYMBOL(rtnl_lock);
 EXPORT_SYMBOL(rtnl_trylock);
 EXPORT_SYMBOL(rtnl_unlock);
+EXPORT_SYMBOL(rtnl_is_locked);
 EXPORT_SYMBOL(rtnl_unicast);
 EXPORT_SYMBOL(rtnl_notify);
 EXPORT_SYMBOL(rtnl_set_sk_err);