Re: [net-next,v2,05/14] net: bridge: mcast: track active state, foreign IGMP/MLD querier disappearance

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---
net: bridge: mcast: track active state, foreign IGMP/MLD querier disappearance

This change ensures that the new multicast active state variable is unset
again after a foreign IGMP/MLD querier has disappeared (default: 255
seconds). If no new, other IGMP/MLD querier took over then we can't
reliably receive IGMP/MLD reports anymore and in turn can't ensure the
completeness of our MDB anymore either.

> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> index d5c623dce7eb..0fc29875db9c 100644
> --- a/net/bridge/br_multicast.c
> +++ b/net/bridge/br_multicast.c
> @@ -1826,6 +1826,10 @@ static void br_multicast_querier_expired(struct net_bridge_mcast *brmctx,
>  	br_multicast_start_querier(brmctx, query);
>
>  out:
> +	/* another IGMP/MLD querier disappeared, set multicast state to inactive
> +	 * if our own querier is disabled, too
> +	 */
> +	br_multicast_update_active(brmctx);
>  	spin_unlock(&brmctx->br->multicast_lock);
>  }

This isn't a bug, but I noticed a couple of unaddressed review comments
from Ido Schimmel's feedback on v1 back in May 2025 that don't appear to
have been incorporated into this v2 series.

In __br_multicast_querier_exists() in net/bridge/br_private.h around line
1164, the 'is_ipv6' bool parameter is marked const. Since this is a
pass-by-value parameter, the const qualifier doesn't provide any benefit.
Should it be removed?

Reference: https://lore.kernel.org/all/aDNPxdmDPYwasUEM@shredder/

Also in br_multicast_querier_exists() in net/bridge/br_private.h around
line 1182, the function takes a struct ethhdr *eth parameter but only uses
eth->h_proto. Would it make more sense to either make the 'eth' parameter
const, or just pass the EtherType (__be16) directly instead of the entire
struct pointer?

Reference: https://lore.kernel.org/all/aDNPxdmDPYwasUEM@shredder/