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

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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



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