netdev - Re: [PATCH net-next v3 2/2] tcp: Free TCP-AO/TCP-MD5 info/keys without RCU

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Message-ID: <20250903162758.2bae802c@kernel.org>
Date: Wed, 3 Sep 2025 16:27:58 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Dmitry Safonov <dima@...sta.com>
Cc: Dmitry Safonov via B4 Relay <devnull+dima.arista.com@...nel.org>, Eric
 Dumazet <edumazet@...gle.com>, Neal Cardwell <ncardwell@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, "David S. Miller"
 <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Bob Gilligan
 <gilligan@...sta.com>, Salam Noureddine <noureddine@...sta.com>, Dmitry
 Safonov <0x7f454c46@...il.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 2/2] tcp: Free TCP-AO/TCP-MD5 info/keys
 without RCU

On Thu, 4 Sep 2025 00:17:34 +0100 Dmitry Safonov wrote:
> > > Right. I'll remove tcp_ao_info::rcu in v4.
> > > For tcp_ao_key it's needed for the regular key rotation, as well as
> > > for tcp_md5sig_key.  
> >
> > Hm, maybe I missed something. I did a test allmodconfig build yesterday
> > and while the md5sig_key rcu was still needed, removing the ao_key
> > didn't cause issues. But it was just a quick test I didn't even config
> > kconfig is sane.  
> 
> Hmm, probably CONFIG_TCP_AO was off?
> tcp_ao_delete_key() does call_rcu(&key->rcu, tcp_ao_key_free_rcu).
> 
> Looking at the code now, I guess what I could have done even more is
> migrating tcp_sock::ao_info (and tcp_timewait_sock::ao_info) from
> rcu_*() helpers to acquire/release ones. Somewhat feeling uneasy about
> going that far just yet. Should I do it with another cleanup on the
> top, what do you think?

No preference :)