From 30940a17e5c54788bec52d9fd9f5317aaa980c8c Mon Sep 17 00:00:00 2001 From: Pengcheng Yang Date: Tue, 2 Aug 2022 21:43:28 +0800 Subject: [PATCH] tcp: fix F-RTO may not work correctly when receiving DSACK stable inclusion from stable-v5.10.114 commit aa138efd2bbf74a5d0cbc96b89f7955407ed9243 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5IY1V Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa138efd2bbf74a5d0cbc96b89f7955407ed9243 -------------------------------- [ Upstream commit d9157f6806d1499e173770df1f1b234763de5c79 ] Currently DSACK is regarded as a dupack, which may cause F-RTO to incorrectly enter "loss was real" when receiving DSACK. Packetdrill to demonstrate: // Enable F-RTO and TLP 0 `sysctl -q net.ipv4.tcp_frto=2` 0 `sysctl -q net.ipv4.tcp_early_retrans=3` 0 `sysctl -q net.ipv4.tcp_congestion_control=cubic` // Establish a connection +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 // RTT 10ms, RTO 210ms +.1 < S 0:0(0) win 32792 +0 > S. 0:0(0) ack 1 <...> +.01 < . 1:1(0) ack 1 win 257 +0 accept(3, ..., ...) = 4 // Send 2 data segments +0 write(4, ..., 2000) = 2000 +0 > P. 1:2001(2000) ack 1 // TLP +.022 > P. 1001:2001(1000) ack 1 // Continue to send 8 data segments +0 write(4, ..., 10000) = 10000 +0 > P. 2001:10001(8000) ack 1 // RTO +.188 > . 1:1001(1000) ack 1 // The original data is acked and new data is sent(F-RTO step 2.b) +0 < . 1:1(0) ack 2001 win 257 +0 > P. 10001:12001(2000) ack 1 // D-SACK caused by TLP is regarded as a dupack, this results in // the incorrect judgment of "loss was real"(F-RTO step 3.a) +.022 < . 1:1(0) ack 2001 win 257 // Never-retransmitted data(3001:4001) are acked and // expect to switch to open state(F-RTO step 3.b) +0 < . 1:1(0) ack 4001 win 257 +0 %{ assert tcpi_ca_state == 0, tcpi_ca_state }% Fixes: e33099f96d99 ("tcp: implement RFC5682 F-RTO") Signed-off-by: Pengcheng Yang Acked-by: Neal Cardwell Tested-by: Neal Cardwell Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/1650967419-2150-1-git-send-email-yangpc@wangsu.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin Signed-off-by: Zheng Zengkai Acked-by: Xie XiuQi --- net/ipv4/tcp_input.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 6748d4d9489d..c10a86c86ad5 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3814,7 +3814,8 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) tcp_process_tlp_ack(sk, ack, flag); if (tcp_ack_is_dubious(sk, flag)) { - if (!(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP))) { + if (!(flag & (FLAG_SND_UNA_ADVANCED | + FLAG_NOT_DUP | FLAG_DSACKING_ACK))) { num_dupack = 1; /* Consider if pure acks were aggregated in tcp_add_backlog() */ if (!(flag & FLAG_DATA)) -- GitLab