netdev - Re: [PATCH net] udp: don't be set unconnected if only UDP cmsg

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Message-ID: <661e9089df8f7_5279f2948e@willemb.c.googlers.com.notmuch>
Date: Tue, 16 Apr 2024 10:51:53 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Yick Xie <yick.xie@...il.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: willemb@...gle.com, 
 netdev@...r.kernel.org, 
 davem@...emloft.net
Subject: Re: [PATCH net] udp: don't be set unconnected if only UDP cmsg

Yick Xie wrote:
> On Mon, Apr 15, 2024 at 10:11 PM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> >
> > Yick Xie wrote:
> > > If "udp_cmsg_send()" returned 0 (i.e. only UDP cmsg),
> > > "connected" should not be set to 0. Otherwise it stops
> > > the connected socket from using the cached route.
> > >
> > > Signed-off-by: Yick Xie <yick.xie@...il.com>
> >
> > This either needs to target net-next, or have
> >
> > Fixes: 2e8de8576343 ("udp: add gso segment cmsg")
> 
> I should have added that, sorry for the mess.

No worries.

> > I think it can be argued either way. This situation existed from the
> > start, and is true for other cmsg that don't affect routing as well.
> >
> > If the impact of the route lookup is significant, it couls be argued
> > to be a performance bug.
> 
> With sendmsg(), any smaller gso_size could be picked up dynamically.
> Then it depends, "ip_route_output_flow()" could be as expensive as
> "ip_make_skb()".
> 
> > I steer towards net-next. In which case it would be nice to also
> > move the ipc.opt branch and perhaps even exclude other common cmsgs,
> > such as SCM_TXTIME and SCM_TIMESTAMPING.
> 
> Both are fine. Though could it be better to take an easy backporting at first?

Sounds good. Please just resend with the Fixes tag.