netdev - Re: [PATCH bpf-next v7 2/8] net: Update an existing TCP congestion control algorithm.

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Message-ID: <ee8cab13-9018-5f62-0415-16409ee1610b@linux.dev>
Date:   Fri, 17 Mar 2023 10:18:19 -0700
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Kui-Feng Lee <kuifeng@...a.com>, bpf@...r.kernel.org,
        ast@...nel.org, song@...nel.org, kernel-team@...a.com,
        andrii@...nel.org, sdf@...gle.com
Subject: Re: [PATCH bpf-next v7 2/8] net: Update an existing TCP congestion
 control algorithm.

On 3/17/23 8:23 AM, Daniel Borkmann wrote:
>  From the function itself what is not clear whether
> callers that replace an existing one should do the synchronize_rcu() themselves 
> or if this should
> be part of tcp_update_congestion_control?

bpf_struct_ops_map_free (in patch 1) also does synchronize_rcu() for another 
reason (bpf_setsockopt), so the caller (bpf_struct_ops) is doing it. From 
looking at tcp_unregister_congestion_control(), make sense that it is more 
correct to have another synchronize_rcu() also in tcp_update_congestion_control 
in case there will be other non bpf_struct_ops caller doing update in the future.