netdev - Re: [PATCH net v1] tcp: Return user_mss for TCP_MAXSEG in CLOSE/LISTEN state if user

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Date: Wed, 24 May 2023 11:51:12 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Cambda Zhu <cambda@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Jason Xing <kerneljasonxing@...il.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Dust Li <dust.li@...ux.alibaba.com>,
	Tony Lu <tonylu@...ux.alibaba.com>,
	Jack Yang <mingliang@...ux.alibaba.com>
Subject: Re: [PATCH net v1] tcp: Return user_mss for TCP_MAXSEG in
 CLOSE/LISTEN state if user_mss set

On Wed, May 24, 2023 at 05:10:54PM +0800, Cambda Zhu wrote:
> 
> > On May 24, 2023, at 16:33, Cambda Zhu <cambda@...ux.alibaba.com> wrote:
> > 
> > This patch replaces the tp->mss_cache check in getting TCP_MAXSEG
> > with tp->rx_opt.user_mss check for CLOSE/LISTEN sock. Since
> > tp->mss_cache is initialized with TCP_MSS_DEFAULT, checking if
> > it's zero is probably a bug.
> > 
> > With this change, getting TCP_MAXSEG before connecting will return
> > default MSS normally, and return user_mss if user_mss is set.
> > 
> > Fixes: 0c409e85f0ac ("Import 2.3.41pre2")
> > Reported-by: Jack Yang <mingliang@...ux.alibaba.com>
> > Suggested-by: Eric Dumazet <edumazet@...gle.com>
> > Link: https://lore.kernel.org/netdev/CANn89i+3kL9pYtkxkwxwNMzvC_w3LNUum_2=3u+UyLBmGmifHA@mail.gmail.com/#t
> > Signed-off-by: Cambda Zhu <cambda@...ux.alibaba.com>
> > Link: https://lore.kernel.org/netdev/14D45862-36EA-4076-974C-EA67513C92F6@linux.alibaba.com/
> > ---
> > v1:
> > - Return default MSS if user_mss not set for backwards compatibility.
> > - Send patch to net instead of net-next, with Fixes tag.
> > - Add Eric's tags.
> > ---
> > net/ipv4/tcp.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 4d6392c16b7a..3e01a58724b8 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -4081,7 +4081,8 @@ int do_tcp_getsockopt(struct sock *sk, int level,
> > switch (optname) {
> > case TCP_MAXSEG:
> > val = tp->mss_cache;
> > - if (!val && ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
> > + if (tp->rx_opt.user_mss &&
> > +    ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
> > val = tp->rx_opt.user_mss;
> > if (tp->repair)
> > val = tp->rx_opt.mss_clamp;
> > -- 
> > 2.16.6
> 
> I see netdev/verify_fixes check failed for the commit 0c409e85f0ac ("Import 2.3.41pre2").
> The commit is from:
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
> 
> Should I remove the Fixes tag?

Hi Cambda Zhu,

AFAIK, that is a tree of historical versions that predate git history,
which began with version v2.6.12-rc2.

If this is a fix for a but ghat has been present since before v2.6.12-rc2
then I think standard practice is to use the initial commit of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

That is:

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

N.B.: I did not check to see if the bug you are fixing has been present
since then. But in any case, the fixes tag in your patch is not correct.

-- 
pw-bot: cr