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Date:   Wed, 9 Sep 2020 17:29:06 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Neal Cardwell <ncardwell@...gle.com>
CC:     David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>, Kevin Yang <yyd@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Lawrence Brakmo <brakmo@...com>
Subject: Re: [PATCH net-next 3/4] tcp: simplify tcp_set_congestion_control():
 always reinitialize

On Wed, Sep 09, 2020 at 02:15:55PM -0400, Neal Cardwell wrote:
> Now that the previous patches ensure that all call sites for
> tcp_set_congestion_control() want to initialize congestion control, we
> can simplify tcp_set_congestion_control() by removing the reinit
> argument and the code to support it.
> 
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
> Acked-by: Kevin Yang <yyd@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Lawrence Brakmo <brakmo@...com>
> ---
>  include/net/tcp.h   |  2 +-
>  net/core/filter.c   |  3 +--
>  net/ipv4/tcp.c      |  2 +-
>  net/ipv4/tcp_cong.c | 11 ++---------
>  4 files changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index e85d564446c6..f857146c17a5 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1104,7 +1104,7 @@ void tcp_get_available_congestion_control(char *buf, size_t len);
>  void tcp_get_allowed_congestion_control(char *buf, size_t len);
>  int tcp_set_allowed_congestion_control(char *allowed);
>  int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
> -			       bool reinit, bool cap_net_admin);
> +			       bool cap_net_admin);
>  u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
>  void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
>  
> diff --git a/net/core/filter.c b/net/core/filter.c
> index b26c04924fa3..0bd0a97ee951 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4451,8 +4451,7 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
>  			strncpy(name, optval, min_t(long, optlen,
>  						    TCP_CA_NAME_MAX-1));
>  			name[TCP_CA_NAME_MAX-1] = 0;
> -			ret = tcp_set_congestion_control(sk, name, false,
> -							 true, true);
> +			ret = tcp_set_congestion_control(sk, name, false, true);
>  		} else {
>  			struct inet_connection_sock *icsk = inet_csk(sk);
>  			struct tcp_sock *tp = tcp_sk(sk);
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 7360d3db2b61..e58ab9db73ff 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3050,7 +3050,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level, int optname,
>  		name[val] = 0;
>  
>  		lock_sock(sk);
> -		err = tcp_set_congestion_control(sk, name, true, true,
> +		err = tcp_set_congestion_control(sk, name, true,
>  						 ns_capable(sock_net(sk)->user_ns,
>  							    CAP_NET_ADMIN));
>  		release_sock(sk);
> diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> index d18d7a1ce4ce..a9b0fb52a1ec 100644
> --- a/net/ipv4/tcp_cong.c
> +++ b/net/ipv4/tcp_cong.c
> @@ -341,7 +341,7 @@ int tcp_set_allowed_congestion_control(char *val)
>   * already initialized.
>   */
>  int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
> -			       bool reinit, bool cap_net_admin)
> +			       bool cap_net_admin)
>  {
>  	struct inet_connection_sock *icsk = inet_csk(sk);
>  	const struct tcp_congestion_ops *ca;
> @@ -365,15 +365,8 @@ int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
>  	if (!ca) {
>  		err = -ENOENT;
>  	} else if (!load) {
nit.

I think this "else if (!load)" case can be completely removed and simply
allow it to fall through to the last
"else { tcp_reinit_congestion_control(sk, ca); }" .

> -		const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
> -
>  		if (bpf_try_module_get(ca, ca->owner)) {
> -			if (reinit) {
> -				tcp_reinit_congestion_control(sk, ca);
> -			} else {
> -				icsk->icsk_ca_ops = ca;
> -				bpf_module_put(old_ca, old_ca->owner);
> -			}
> +			tcp_reinit_congestion_control(sk, ca);
>  		} else {
>  			err = -EBUSY;
>  		}
> -- 
> 2.28.0.526.ge36021eeef-goog
> 

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