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net: tcp: send zero-window ACK when no memory 

For now, skb will be dropped when no memory, which makes client keep
retrans util timeout and it's not friendly to the users.

In this patch, we reply an ACK with zero-window in this case to update
the snd_wnd of the sender to 0. Therefore, the sender won't timeout the
connection and will probe the zero-window with the retransmits.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Menglong Dong 2023-08-11 10:55:27 +08:00 committed by David S. Miller
parent 3e6860ec3a
commit e2142825c1
3 changed files with 25 additions and 10 deletions
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3
include/net/inet_connection_sock.h
View File

@ -164,7 +164,8 @@ enum inet_csk_ack_state_t {
ICSK_ACK_TIMER = 2,
ICSK_ACK_PUSHED = 4,
ICSK_ACK_PUSHED2 = 8,
ICSK_ACK_NOW = 16 /* Send the next ACK immediately (once) */
ICSK_ACK_NOW = 16, /* Send the next ACK immediately (once) */
ICSK_ACK_NOMEM = 32,
};
void inet_csk_init_xmit_timers(struct sock *sk,

18
net/ipv4/tcp_input.c
View File

@ -5059,13 +5059,19 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
/* Ok. In sequence. In window. */
queue_and_out:
if (skb_queue_len(&sk->sk_receive_queue) == 0)
sk_forced_mem_schedule(sk, skb->truesize);
else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
reason = SKB_DROP_REASON_PROTO_MEM;
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
/* TODO: maybe ratelimit these WIN 0 ACK ? */
inet_csk(sk)->icsk_ack.pending |=
(ICSK_ACK_NOMEM | ICSK_ACK_NOW);
inet_csk_schedule_ack(sk);
sk->sk_data_ready(sk);
goto drop;
if (skb_queue_len(&sk->sk_receive_queue)) {
reason = SKB_DROP_REASON_PROTO_MEM;
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
goto drop;
}
sk_forced_mem_schedule(sk, skb->truesize);
}
eaten = tcp_queue_rcv(sk, skb, &fragstolen);

14
net/ipv4/tcp_output.c
View File

@ -257,11 +257,19 @@ EXPORT_SYMBOL(tcp_select_initial_window);
static u16 tcp_select_window(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 old_win = tp->rcv_wnd;
u32 cur_win = tcp_receive_window(tp);
u32 new_win = __tcp_select_window(sk);
struct net *net = sock_net(sk);
u32 old_win = tp->rcv_wnd;
u32 cur_win, new_win;
/* Make the window 0 if we failed to queue the data because we
* are out of memory. The window is temporary, so we don't store
* it on the socket.
*/
if (unlikely(inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOMEM))
return 0;
cur_win = tcp_receive_window(tp);
new_win = __tcp_select_window(sk);
if (new_win < cur_win) {
/* Danger Will Robinson!
* Don't update rcv_wup/rcv_wnd here or else