linux-kernel - Re: [PATCH net v2 1/2] net: ipv4: fix incorrect MTU in broadcast routes

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Message-ID: <20250708185430.68f143a2@kernel.org>
Date: Tue, 8 Jul 2025 18:54:30 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Oscar Maes <oscmaes92@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, dsahern@...nel.org,
 edumazet@...gle.com, pabeni@...hat.com, horms@...nel.org,
 stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2 1/2] net: ipv4: fix incorrect MTU in broadcast
 routes

On Thu,  3 Jul 2025 17:28:37 +0200 Oscar Maes wrote:
>  	if (type == RTN_BROADCAST) {
>  		flags |= RTCF_BROADCAST | RTCF_LOCAL;
> -		fi = NULL;
>  	} else if (type == RTN_MULTICAST) {
>  		flags |= RTCF_MULTICAST | RTCF_LOCAL;
>  		if (!ip_check_mc_rcu(in_dev, fl4->daddr, fl4->saddr,

Not super familiar with this code, but do we not need to set 
do_cache = false; ? I'm guessing cache interactions may have
been the reason fib_info was originally cleared, not sure if
that's still relevant..

I'd also target this at net-next, unless you can pinpoint
some kernel version where MTU on bcast routes worked..
-- 
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