linux-kernel - Re: [PATCH v3 net] net: bridge: Do not offload IGMP/MLD messages

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Message-ID: <aHfL5kwwd72U5zGh@shredder>
Date: Wed, 16 Jul 2025 18:57:26 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Joseph Huang <Joseph.Huang@...min.com>
Cc: netdev@...r.kernel.org, Joseph Huang <joseph.huang.2024@...il.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Tobias Waldekranz <tobias@...dekranz.com>, bridge@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net] net: bridge: Do not offload IGMP/MLD messages

On Wed, Jul 16, 2025 at 11:35:50AM -0400, Joseph Huang wrote:
> Do not offload IGMP/MLD messages as it could lead to IGMP/MLD Reports
> being unintentionally flooded to Hosts. Instead, let the bridge decide
> where to send these IGMP/MLD messages.
> 
> Consider the case where the local host is sending out reports in response
> to a remote querier like the following:
> 
>        mcast-listener-process (IP_ADD_MEMBERSHIP)
>           \
>           br0
>          /   \
>       swp1   swp2
>         |     |
>   QUERIER     SOME-OTHER-HOST
> 
> In the above setup, br0 will want to br_forward() reports for
> mcast-listener-process's group(s) via swp1 to QUERIER; but since the
> source hwdom is 0, the report is eligible for tx offloading, and is
> flooded by hardware to both swp1 and swp2, reaching SOME-OTHER-HOST as
> well. (Example and illustration provided by Tobias.)
> 
> Fixes: 472111920f1c ("net: bridge: switchdev: allow the TX data plane forwarding to be offloaded")
> Signed-off-by: Joseph Huang <Joseph.Huang@...min.com>

Reviewed-by: Ido Schimmel <idosch@...dia.com>