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tcp: fix mishandling when the sack compression is deferred.

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[ Upstream commit 30c6f0bf95 ]

In this patch, we mainly try to handle sending a compressed ack
correctly if it's deferred.

Here are more details in the old logic:
When sack compression is triggered in the tcp_compressed_ack_kick(),
if the sock is owned by user, it will set TCP_DELACK_TIMER_DEFERRED
and then defer to the release cb phrase. Later once user releases
the sock, tcp_delack_timer_handler() should send a ack as expected,
which, however, cannot happen due to lack of ICSK_ACK_TIMER flag.
Therefore, the receiver would not sent an ack until the sender's
retransmission timeout. It definitely increases unnecessary latency.

Fixes: 5d9f4262b7 ("tcp: add SACK compression")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: fuyuanli <fuyuanli@didiglobal.com>
Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://lore.kernel.org/netdev/20230529113804.GA20300@didi-ThinkCentre-M920t-N000/
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230531080150.GA20424@didi-ThinkCentre-M920t-N000
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
fuyuanli 2023-05-31 16:01:50 +08:00 committed by Greg Kroah-Hartman
parent 900fab73a9
commit b666755aab
3 changed files with 15 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
include/net/tcp.h
View file

@ -632,6 +632,7 @@ void tcp_reset(struct sock *sk, struct sk_buff *skb);
void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb);
void tcp_fin(struct sock *sk);
void tcp_check_space(struct sock *sk);
void tcp_sack_compress_send_ack(struct sock *sk);
/* tcp_timer.c */
void tcp_init_xmit_timers(struct sock *);

2
net/ipv4/tcp_input.c
View file

@ -4530,7 +4530,7 @@ static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
}
}
static void tcp_sack_compress_send_ack(struct sock *sk)
void tcp_sack_compress_send_ack(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);

16
net/ipv4/tcp_timer.c
View file

@ -290,9 +290,19 @@ static int tcp_write_timeout(struct sock *sk)
void tcp_delack_timer_handler(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
!(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
return;
/* Handling the sack compression case */
if (tp->compressed_ack) {
tcp_mstamp_refresh(tp);
tcp_sack_compress_send_ack(sk);
return;
}
if (!(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
return;
if (time_after(icsk->icsk_ack.timeout, jiffies)) {
@ -312,7 +322,7 @@ void tcp_delack_timer_handler(struct sock *sk)
inet_csk_exit_pingpong_mode(sk);
icsk->icsk_ack.ato = TCP_ATO_MIN;
}
tcp_mstamp_refresh(tcp_sk(sk));
tcp_mstamp_refresh(tp);
tcp_send_ack(sk);
__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
}