Re: [PATCH net-next] net: bridge: mcast: fix unused br var when lockdep isn't defined

On 8 September 2020 19:00:49 EEST, Jakub Kicinski [off-list ref] wrote:

On Tue,  8 Sep 2020 10:17:13 +0300 Nikolay Aleksandrov wrote:

quoted

Stephen reported the following warning:
 net/bridge/br_multicast.c: In function 'br_multicast_find_port':
 net/bridge/br_multicast.c:1818:21: warning: unused variable 'br'

[-Wunused-variable]

quoted

  1818 |  struct net_bridge *br = mp->br;
       |                     ^~

It happens due to bridge's mlock_dereference() when lockdep isn't

defined.

quoted

Silence the warning by annotating the variable as __maybe_unused.

Fixes: 0436862e417e ("net: bridge: mcast: support for IGMPv3/MLDv2

ALLOW_NEW_SOURCES report")

quoted

Reported-by: Stephen Rothwell <redacted>
Signed-off-by: Nikolay Aleksandrov <redacted>
---
 net/bridge/br_multicast.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index b83f11228948..33adf44ef7ec 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c

@@ -1814,8 +1814,8 @@ br_multicast_find_port(struct

net_bridge_mdb_entry *mp,

quoted

 		       struct net_bridge_port *p,
 		       const unsigned char *src)
 {
+	struct net_bridge *br __maybe_unused = mp->br;
 	struct net_bridge_port_group *pg;
-	struct net_bridge *br = mp->br;
 
 	for (pg = mlock_dereference(mp->ports, br);
 	     pg;

That's a lazy fix :( Is everyone using lockdep annotations going to
sprinkle __maybe_unused throughout the code? Macros should also always
evaluate their arguments.

When the local variable's only used for lockdep, I guess. :) 
Here we don't actually need it at all, alternatively we can just drop it and use mp->br.