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

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Date:   Tue, 8 Sep 2020 09:00:49 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, roopa@...dia.com,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH net-next] net: bridge: mcast: fix unused br var when
 lockdep isn't defined

On Tue,  8 Sep 2020 10:17:13 +0300 Nikolay Aleksandrov wrote:
> 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]
>   1818 |  struct net_bridge *br = mp->br;
>        |                     ^~
> 
> It happens due to bridge's mlock_dereference() when lockdep isn't defined.
> Silence the warning by annotating the variable as __maybe_unused.
> 
> Fixes: 0436862e417e ("net: bridge: mcast: support for IGMPv3/MLDv2 ALLOW_NEW_SOURCES report")
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> ---
>  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,
>  		       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.