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

On Tue, Jul 08, 2025 at 06:54:30PM -0700, Jakub Kicinski wrote:

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.. -- pw-bot: cr

The caching mechanism was introduced after this line, back when nhc was embedded in fib_info. (see https://lore.kernel.org/netdev/20120720.142612.691540831359186107.davem@dave...)

I'll resend to net-next.