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0e24d17bd9
By default, the Linux TCP implementation does not shrink the advertised window (RFC 7323 calls this "window retraction") with the following exceptions: - When an incoming segment cannot be added due to the receive buffer running out of memory. Since commit8c670bdfa5("tcp: correct handling of extreme memory squeeze") a zero window will be advertised in this case. It turns out that reaching the required memory pressure is easy when window scaling is in use. In the simplest case, sending a sufficient number of segments smaller than the scale factor to a receiver that does not read data is enough. - Commitb650d953cd("tcp: enforce receive buffer memory limits by allowing the tcp window to shrink") addressed the "eating memory" problem by introducing a sysctl knob that allows shrinking the window before running out of memory. However, RFC 7323 does not only state that shrinking the window is necessary in some cases, it also formulates requirements for TCP implementations when doing so (Section 2.4). This commit addresses the receiver-side requirements: After retracting the window, the peer may have a snd_nxt that lies within a previously advertised window but is now beyond the retracted window. This means that all incoming segments (including pure ACKs) will be rejected until the application happens to read enough data to let the peer's snd_nxt be in window again (which may be never). To comply with RFC 7323, the receiver MUST honor any segment that would have been in window for any ACK sent by the receiver and, when window scaling is in effect, SHOULD track the maximum window sequence number it has advertised. This patch tracks that maximum window sequence number rcv_mwnd_seq throughout the connection and uses it in tcp_sequence() when deciding whether a segment is acceptable. rcv_mwnd_seq is updated together with rcv_wup and rcv_wnd in tcp_select_window(). If we count tcp_sequence() as fast path, it is read in the fast path. Therefore, rcv_mwnd_seq is put into rcv_wnd's cacheline group. The logic for handling received data in tcp_data_queue() is already sufficient and does not need to be updated. Signed-off-by: Simon Baatz <gmbnomis@gmail.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-1-4c7f96b1ec69@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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173 lines
16 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. Copyright (C) 2023 Google LLC
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=========================================
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tcp_sock struct fast path usage breakdown
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=========================================
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============================= ======================= =================== =================== ==================================================================================================================================================================================================================
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Type Name fastpath_tx_access fastpath_rx_access Comments
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============================= ======================= =================== =================== ==================================================================================================================================================================================================================
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struct inet_connection_sock inet_conn
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u16 tcp_header_len read_mostly read_mostly tcp_bound_to_half_wnd,tcp_current_mss(tx);tcp_rcv_established(rx)
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u16 gso_segs read_mostly tcp_xmit_size_goal
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__be32 pred_flags read_write read_mostly tcp_select_window(tx);tcp_rcv_established(rx)
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u64 bytes_received read_write tcp_rcv_nxt_update(rx)
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u32 segs_in read_write tcp_v6_rcv(rx)
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u32 data_segs_in read_write tcp_v6_rcv(rx)
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u32 rcv_nxt read_mostly read_write tcp_cleanup_rbuf,tcp_send_ack,tcp_inq_hint,tcp_transmit_skb,tcp_receive_window(tx);tcp_v6_do_rcv,tcp_rcv_established,tcp_data_queue,tcp_receive_window,tcp_rcv_nxt_update(write)(rx)
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u32 copied_seq read_mostly tcp_cleanup_rbuf,tcp_rcv_space_adjust,tcp_inq_hint
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u32 rcv_wup read_write __tcp_cleanup_rbuf,tcp_receive_window,tcp_receive_established
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u32 snd_nxt read_write read_mostly tcp_rate_check_app_limited,__tcp_transmit_skb,tcp_event_new_data_sent(write)(tx);tcp_rcv_established,tcp_ack,tcp_clean_rtx_queue(rx)
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u32 segs_out read_write __tcp_transmit_skb
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u32 data_segs_out read_write __tcp_transmit_skb,tcp_update_skb_after_send
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u64 bytes_sent read_write __tcp_transmit_skb
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u64 bytes_acked read_write tcp_snd_una_update/tcp_ack
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u32 dsack_dups
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u32 snd_una read_mostly read_write tcp_wnd_end,tcp_urg_mode,tcp_minshall_check,tcp_cwnd_validate(tx);tcp_ack,tcp_may_update_window,tcp_clean_rtx_queue(write),tcp_ack_tstamp(rx)
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u32 snd_sml read_write tcp_minshall_check,tcp_minshall_update
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u32 rcv_tstamp read_write read_write tcp_ack
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void * tcp_clean_acked read_mostly tcp_ack
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u32 lsndtime read_write tcp_slow_start_after_idle_check,tcp_event_data_sent
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u32 last_oow_ack_time
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u32 compressed_ack_rcv_nxt
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u32 tsoffset read_mostly read_mostly tcp_established_options(tx);tcp_fast_parse_options(rx)
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struct list_head tsq_node
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struct list_head tsorted_sent_queue read_write tcp_update_skb_after_send
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u32 snd_wl1 read_mostly tcp_may_update_window
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u32 snd_wnd read_mostly read_mostly tcp_wnd_end,tcp_tso_should_defer(tx);tcp_fast_path_on(rx)
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u32 max_window read_mostly tcp_bound_to_half_wnd,forced_push
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u32 mss_cache read_mostly read_mostly tcp_rate_check_app_limited,tcp_current_mss,tcp_sync_mss,tcp_sndbuf_expand,tcp_tso_should_defer(tx);tcp_update_pacing_rate,tcp_clean_rtx_queue(rx)
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u32 window_clamp read_mostly read_write tcp_rcv_space_adjust,__tcp_select_window
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u32 rcv_ssthresh read_mostly __tcp_select_window
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u8 scaling_ratio read_mostly read_mostly tcp_win_from_space
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struct tcp_rack
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u16 advmss read_mostly tcp_rcv_space_adjust
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u8 compressed_ack
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u8:2 dup_ack_counter
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u8:1 tlp_retrans
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u8:1 tcp_usec_ts read_mostly read_mostly
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u32 chrono_start read_write tcp_chrono_start/stop(tcp_write_xmit,tcp_cwnd_validate,tcp_send_syn_data)
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u32[3] chrono_stat read_write tcp_chrono_start/stop(tcp_write_xmit,tcp_cwnd_validate,tcp_send_syn_data)
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u8:2 chrono_type read_write tcp_chrono_start/stop(tcp_write_xmit,tcp_cwnd_validate,tcp_send_syn_data)
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u8:1 rate_app_limited read_write tcp_rate_gen
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u8:1 fastopen_connect
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u8:1 fastopen_no_cookie
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u8:1 is_sack_reneg read_mostly tcp_skb_entail,tcp_ack
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u8:2 fastopen_client_fail
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u8:4 nonagle read_write tcp_skb_entail,tcp_push_pending_frames
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u8:1 thin_lto
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u8:1 recvmsg_inq read_mostly tcp_recvmsg
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u8:1 repair read_mostly tcp_write_xmit
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u8:1 frto
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u8 repair_queue
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u8:2 save_syn
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u8:1 syn_data
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u8:1 syn_fastopen
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u8:1 syn_fastopen_exp
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u8:1 syn_fastopen_ch
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u8:1 syn_data_acked
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u8:1 is_cwnd_limited read_mostly tcp_cwnd_validate,tcp_is_cwnd_limited
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u32 tlp_high_seq read_mostly tcp_ack
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u32 tcp_tx_delay
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u64 tcp_wstamp_ns read_write tcp_pacing_check,tcp_tso_should_defer,tcp_update_skb_after_send
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u64 tcp_clock_cache read_write read_write tcp_mstamp_refresh(tcp_write_xmit/tcp_rcv_space_adjust),__tcp_transmit_skb,tcp_tso_should_defer;timer
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u64 tcp_mstamp read_write read_write tcp_mstamp_refresh(tcp_write_xmit/tcp_rcv_space_adjust)(tx);tcp_rcv_space_adjust,tcp_rate_gen,tcp_clean_rtx_queue,tcp_ack_update_rtt/tcp_time_stamp(rx);timer
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u32 srtt_us read_mostly read_write tcp_tso_should_defer(tx);tcp_update_pacing_rate,__tcp_set_rto,tcp_rtt_estimator(rx)
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u32 mdev_us read_write tcp_rtt_estimator
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u32 mdev_max_us
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u32 rttvar_us read_mostly __tcp_set_rto
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u32 rtt_seq read_write tcp_rtt_estimator
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struct minmax rtt_min read_mostly tcp_min_rtt/tcp_rate_gen,tcp_min_rtttcp_update_rtt_min
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u32 packets_out read_write read_write tcp_packets_in_flight(tx/rx);tcp_slow_start_after_idle_check,tcp_nagle_check,tcp_rate_skb_sent,tcp_event_new_data_sent,tcp_cwnd_validate,tcp_write_xmit(tx);tcp_ack,tcp_clean_rtx_queue,tcp_update_pacing_rate(rx)
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u32 retrans_out read_mostly tcp_packets_in_flight,tcp_rate_check_app_limited
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u32 max_packets_out read_write tcp_cwnd_validate
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u32 cwnd_usage_seq read_write tcp_cwnd_validate
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u16 urg_data read_mostly tcp_fast_path_check
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u8 ecn_flags read_write tcp_ecn_send
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u8 keepalive_probes
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u32 reordering read_mostly tcp_sndbuf_expand
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u32 reord_seen
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u32 snd_up read_write read_mostly tcp_mark_urg,tcp_urg_mode,__tcp_transmit_skb(tx);tcp_clean_rtx_queue(rx)
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struct tcp_options_received rx_opt read_mostly read_write tcp_established_options(tx);tcp_fast_path_on,tcp_ack_update_window,tcp_is_sack,tcp_data_queue,tcp_rcv_established,tcp_ack_update_rtt(rx)
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u32 snd_ssthresh read_mostly tcp_update_pacing_rate
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u32 snd_cwnd read_mostly read_mostly tcp_snd_cwnd,tcp_rate_check_app_limited,tcp_tso_should_defer(tx);tcp_update_pacing_rate
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u32 snd_cwnd_cnt
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u32 snd_cwnd_clamp
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u32 snd_cwnd_used
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u32 snd_cwnd_stamp
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u32 prior_cwnd
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u32 prr_delivered
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u32 prr_out read_mostly read_mostly tcp_rate_skb_sent,tcp_newly_delivered(tx);tcp_ack,tcp_rate_gen,tcp_clean_rtx_queue(rx)
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u32 delivered read_mostly read_write tcp_rate_skb_sent, tcp_newly_delivered(tx);tcp_ack, tcp_rate_gen, tcp_clean_rtx_queue (rx)
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u32 delivered_ce read_mostly read_write tcp_rate_skb_sent(tx);tcp_rate_gen(rx)
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u32 received_ce read_mostly read_write
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u32[3] received_ecn_bytes read_mostly read_write
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u8:4 received_ce_pending read_mostly read_write
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u32[3] delivered_ecn_bytes read_write
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u16 pkts_acked_ewma read_write
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u8:2 syn_ect_snt write_mostly read_write
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u8:2 syn_ect_rcv read_mostly read_write
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u8:2 accecn_minlen write_mostly read_write
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u8:2 est_ecnfield read_write
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u8:2 accecn_opt_demand read_mostly read_write
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u8:2 prev_ecnfield read_write
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u64 accecn_opt_tstamp read_write
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u8:4 accecn_fail_mode
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u32 lost read_mostly tcp_ack
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u32 app_limited read_write read_mostly tcp_rate_check_app_limited,tcp_rate_skb_sent(tx);tcp_rate_gen(rx)
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u64 first_tx_mstamp read_write tcp_rate_skb_sent
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u64 delivered_mstamp read_write tcp_rate_skb_sent
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u32 rate_delivered read_mostly tcp_rate_gen
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u32 rate_interval_us read_mostly rate_delivered,rate_app_limited
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u32 rcv_wnd read_write read_mostly tcp_select_window,tcp_receive_window,tcp_fast_path_check
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u32 rcv_mwnd_seq read_write tcp_select_window
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u32 write_seq read_write tcp_rate_check_app_limited,tcp_write_queue_empty,tcp_skb_entail,forced_push,tcp_mark_push
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u32 notsent_lowat read_mostly tcp_stream_memory_free
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u32 pushed_seq read_write tcp_mark_push,forced_push
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u32 lost_out read_mostly read_mostly tcp_left_out(tx);tcp_packets_in_flight(tx/rx);tcp_rate_check_app_limited(rx)
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u32 sacked_out read_mostly read_mostly tcp_left_out(tx);tcp_packets_in_flight(tx/rx);tcp_clean_rtx_queue(rx)
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struct hrtimer pacing_timer
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struct hrtimer compressed_ack_timer
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struct sk_buff* retransmit_skb_hint read_mostly tcp_clean_rtx_queue
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struct rb_root out_of_order_queue read_mostly tcp_data_queue,tcp_fast_path_check
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struct sk_buff* ooo_last_skb
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struct tcp_sack_block[1] duplicate_sack
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struct tcp_sack_block[4] selective_acks
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struct tcp_sack_block[4] recv_sack_cache
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struct sk_buff* highest_sack read_write tcp_event_new_data_sent
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u32 prior_ssthresh
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u32 high_seq
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u32 retrans_stamp
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u32 undo_marker
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int undo_retrans
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u64 bytes_retrans
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u32 total_retrans
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u32 rto_stamp
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u16 total_rto
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u16 total_rto_recoveries
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u32 total_rto_time
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u32 urg_seq
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unsigned_int keepalive_time
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unsigned_int keepalive_intvl
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int linger2
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u8 bpf_sock_ops_cb_flags
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u8:1 bpf_chg_cc_inprogress
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u16 timeout_rehash
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u32 rcv_ooopack
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u32 rcv_rtt_last_tsecr
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struct rcv_rtt_est read_write tcp_rcv_space_adjust,tcp_rcv_established
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struct rcvq_space read_write tcp_rcv_space_adjust
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struct mtu_probe
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u32 plb_rehash
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u32 mtu_info
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bool is_mptcp
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bool smc_hs_congested
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bool syn_smc
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struct tcp_sock_af_ops* af_specific
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struct tcp_md5sig_info* md5sig_info
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struct tcp_fastopen_request* fastopen_req
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struct request_sock* fastopen_rsk
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struct saved_syn* saved_syn
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============================= ======================= =================== =================== ==================================================================================================================================================================================================================
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