netdev - Re: [PATCH] net: bridge: multicast: notify switchdev driver whenever MC processing gets disabled

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Date:   Tue, 15 Feb 2022 15:34:56 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Oleksandr Mazur <oleksandr.mazur@...ision.eu>
Cc:     netdev@...r.kernel.org, Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        bridge@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: bridge: multicast: notify switchdev driver whenever
 MC processing gets disabled

On Fri, Feb 11, 2022 at 03:14:26PM +0200, Oleksandr Mazur wrote:
> Whenever bridge driver hits the max capacity of MDBs, it disables
> the MC processing (by setting corresponding bridge option), but never
> notifies switchdev about such change (the notifiers are called only upon
> explicit setting of this option, through the registered netlink interface).
> 
> This could lead to situation when Software MDB processing gets disabled,
> but this event never gets offloaded to the underlying Hardware.
> 
> Fix this by adding a notify message in such case.
> 
> Signed-off-by: Oleksandr Mazur <oleksandr.mazur@...ision.eu>
> ---
>  net/bridge/br_multicast.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> index de2409889489..d53c08906bc8 100644
> --- a/net/bridge/br_multicast.c
> +++ b/net/bridge/br_multicast.c
> @@ -82,6 +82,9 @@ static void br_multicast_find_del_pg(struct net_bridge *br,
>  				     struct net_bridge_port_group *pg);
>  static void __br_multicast_stop(struct net_bridge_mcast *brmctx);
>  
> +static int br_mc_disabled_update(struct net_device *dev, bool value,
> +				 struct netlink_ext_ack *extack);
> +
>  static struct net_bridge_port_group *
>  br_sg_port_find(struct net_bridge *br,
>  		struct net_bridge_port_group_sg_key *sg_p)
> @@ -1156,6 +1159,8 @@ struct net_bridge_mdb_entry *br_multicast_new_group(struct net_bridge *br,
>  		return mp;
>  
>  	if (atomic_read(&br->mdb_hash_tbl.nelems) >= br->hash_max) {
> +		err = br_mc_disabled_update(br->dev, false, NULL);
> +		WARN_ON(err && err != -EOPNOTSUPP);

What is the purpose of the WARN_ON()? There are a lot of operations that
can fail in rollback paths, but we never WARN_ON() there

I suggest:

br_mc_disabled_update(br->dev, false, NULL);

>  		br_opt_toggle(br, BROPT_MULTICAST_ENABLED, false);
>  		return ERR_PTR(-E2BIG);
>  	}
> -- 
> 2.17.1
>