Re: [PATCH v2 11/25] tcp: authopt: Implement Sequence Number Extension

[Leonard Crestez]

On 11/1/21 10:54 PM, Eric Dumazet wrote:
> On 11/1/21 9:34 AM, Leonard Crestez wrote:
> > Add a compute_sne function which finds the value of SNE for a certain
> > SEQ given an already known "recent" SNE/SEQ. This is implemented using
> > the standard tcp before/after macro and will work for SEQ values that
> > are without 2^31 of the SEQ for which we know the SNE.
>
> >   }
> > +void __tcp_authopt_update_rcv_sne(struct tcp_sock *tp, struct tcp_authopt_info *info, u32 seq);
> > +static inline void tcp_authopt_update_rcv_sne(struct tcp_sock *tp, u32 seq)
> > +{
> > +	struct tcp_authopt_info *info;
> > +
> > +	if (static_branch_unlikely(&tcp_authopt_needed)) {
> > +		rcu_read_lock();
> > +		info = rcu_dereference(tp->authopt_info);
> > +		if (info)
> > +			__tcp_authopt_update_rcv_sne(tp, info, seq);
> > +		rcu_read_unlock();
> > +	}
> > +}
> > +void __tcp_authopt_update_snd_sne(struct tcp_sock *tp, struct tcp_authopt_info *info, u32 seq);
> > +static inline void tcp_authopt_update_snd_sne(struct tcp_sock *tp, u32 seq)
> > +{
> > +	struct tcp_authopt_info *info;
> > +
> > +	if (static_branch_unlikely(&tcp_authopt_needed)) {
> > +		rcu_read_lock();
> > +		info = rcu_dereference(tp->authopt_info);
> > +		if (info)
> > +			__tcp_authopt_update_snd_sne(tp, info, seq);
> > +		rcu_read_unlock();
> > +	}
> > +}
>
> I would think callers of these helpers own socket lock,
> so no rcu_read_lock()/unlock() should be needed.
>
> Perhaps instead
> rcu_dereference_protected(tp->authopt_info, lockdep_sock_is_held(sk));

Yes, all the callers hold the socket lock and replacing rcu_read_lock 
doesn't trigger any RCU warnings.

--
Regards,
Leonard