tcp: Only init congestion control if not initialized already (8919a9b3) · Commits · 戴 / test

Change tcp_init_transfer() to only initialize congestion control if it has not been initialized already. With this new approach, we can arrange things so that if the EBPF code sets the congestion control by calling setsockopt(TCP_CONGESTION) then tcp_init_transfer() will not re-initialize the CC module. This is an approach that has the following beneficial properties: (1) This allows CC module customizations made by the EBPF called in tcp_init_transfer() to persist, and not be wiped out by a later call to tcp_init_congestion_control() in tcp_init_transfer(). (2) Does not flip the order of EBPF and CC init, to avoid causing bugs for existing code upstream that depends on the current order. (3) Does not cause 2 initializations for for CC in the case where the EBPF called in tcp_init_transfer() wants to set the CC to a new CC algorithm. (4) Allows follow-on simplifications to the code in net/core/filter.c and net/ipv4/tcp_cong.c, which currently both have some complexity to special-case CC initialization to avoid double CC initialization if EBPF sets the CC. Signed-off-by:

Neal Cardwell <ncardwell@google.com> Signed-off-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Acked-by:

Yuchung Cheng <ycheng@google.com> Acked-by:

Kevin Yang <yyd@google.com> Cc: Lawrence Brakmo <brakmo@fb.com>

include/net/inet_connection_sock.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -96,7 +96,8 @@ struct inet_connection_sock {
		void (icsk_clean_acked)(struct sock sk, u32 acked_seq);
		struct hlist_node icsk_listen_portaddr_node;
		unsigned int (icsk_sync_mss)(struct sock sk, u32 pmtu);
		__u8 icsk_ca_state:6,
		__u8 icsk_ca_state:5,
		icsk_ca_initialized:1,
		icsk_ca_setsockopt:1,
		icsk_ca_dst_locked:1;
		__u8 icsk_retransmits;

net/ipv4/tcp.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -2698,6 +2698,7 @@ int tcp_disconnect(struct sock *sk, int flags)
		if (icsk->icsk_ca_ops->release)
		icsk->icsk_ca_ops->release(sk);
		memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
		icsk->icsk_ca_initialized = 0;
		tcp_set_ca_state(sk, TCP_CA_Open);
		tp->is_sack_reneg = 0;
		tcp_clear_retrans(tp);

net/ipv4/tcp_cong.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -176,7 +176,7 @@ void tcp_assign_congestion_control(struct sock *sk)

		void tcp_init_congestion_control(struct sock *sk)
		{
		const struct inet_connection_sock *icsk = inet_csk(sk);
		struct inet_connection_sock *icsk = inet_csk(sk);

		tcp_sk(sk)->prior_ssthresh = 0;
		if (icsk->icsk_ca_ops->init)
		@@ -185,6 +185,7 @@ void tcp_init_congestion_control(struct sock *sk)
		INET_ECN_xmit(sk);
		else
		INET_ECN_dontxmit(sk);
		icsk->icsk_ca_initialized = 1;
		}

		static void tcp_reinit_congestion_control(struct sock *sk,

net/ipv4/tcp_input.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -5894,7 +5894,9 @@ void tcp_init_transfer(struct sock sk, int bpf_op, struct sk_buff skb)
		tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
		tp->snd_cwnd_stamp = tcp_jiffies32;

		icsk->icsk_ca_initialized = 0;
		bpf_skops_established(sk, bpf_op, skb);
		if (!icsk->icsk_ca_initialized)
		tcp_init_congestion_control(sk);
		tcp_init_buffer_space(sk);
		}

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