tcp: Adjust clamping window for applications specifying SO_RCVBUF
tp->scaling_ratio is not updated based on skb->len/skb->truesize once SO_RCVBUF is set leading to the maximum window scaling to be 25% of rcvbuf after commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale") and 50% of rcvbuf after commit 697a6c8cec03 ("tcp: increase the default TCP scaling ratio"). 50% tries to emulate the behavior of older kernels using sysctl_tcp_adv_win_scale with default value. Systems which were using a different values of sysctl_tcp_adv_win_scale in older kernels ended up seeing reduced download speeds in certain cases as covered in https://lists.openwall.net/netdev/2024/05/15/13 While the sysctl scheme is no longer acceptable, the value of 50% is a bit conservative when the skb->len/skb->truesize ratio is later determined to be ~0.66. Applications not specifying SO_RCVBUF update the window scaling and the receiver buffer every time data is copied to userspace. This computation is now used for applications setting SO_RCVBUF to update the maximum window scaling while ensuring that the receive buffer is within the application specified limit. Fixes: dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale") Signed-off-by: Sean Tranchetti <quic_stranche@quicinc.com> Signed-off-by: Subash Abhinov Kasiviswanathan <quic_subashab@quicinc.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -754,8 +754,7 @@ void tcp_rcv_space_adjust(struct sock *sk)
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* <prev RTT . ><current RTT .. ><next RTT .... >
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*/
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if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
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!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
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if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)) {
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u64 rcvwin, grow;
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int rcvbuf;
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@ -771,12 +770,22 @@ void tcp_rcv_space_adjust(struct sock *sk)
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rcvbuf = min_t(u64, tcp_space_from_win(sk, rcvwin),
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READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
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if (rcvbuf > sk->sk_rcvbuf) {
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WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
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if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
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if (rcvbuf > sk->sk_rcvbuf) {
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WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
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/* Make the window clamp follow along. */
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WRITE_ONCE(tp->window_clamp,
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tcp_win_from_space(sk, rcvbuf));
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/* Make the window clamp follow along. */
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WRITE_ONCE(tp->window_clamp,
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tcp_win_from_space(sk, rcvbuf));
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}
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} else {
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/* Make the window clamp follow along while being bounded
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* by SO_RCVBUF.
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*/
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int clamp = tcp_win_from_space(sk, min(rcvbuf, sk->sk_rcvbuf));
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if (clamp > tp->window_clamp)
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WRITE_ONCE(tp->window_clamp, clamp);
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}
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}
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tp->rcvq_space.space = copied;
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