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

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Date:   Tue, 2 Nov 2021 11:50:46 +0200
From:   Leonard Crestez <cdleonard@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Francesco Ruggeri <fruggeri@...sta.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        David Ahern <dsahern@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Christoph Paasch <cpaasch@...le.com>,
        Ivan Delalande <colona@...sta.com>,
        Priyaranjan Jha <priyarjha@...gle.com>, netdev@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v2 11/25] tcp: authopt: Implement Sequence Number
 Extension

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