6.6-stable review patch. If anyone has any objections, please let me know.
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From: Subash Abhinov Kasiviswanathan quic_subashab@quicinc.com
[ Upstream commit 05f76b2d634e65ab34472802d9b142ea9e03f74e ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_input.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 13464e35d7565..d0364cff65c9f 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -748,8 +748,7 @@ void tcp_rcv_space_adjust(struct sock *sk) * <prev RTT . ><current RTT .. ><next RTT .... > */
- if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) && - !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { + if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)) { u64 rcvwin, grow; int rcvbuf;
@@ -765,12 +764,22 @@ void tcp_rcv_space_adjust(struct sock *sk)
rcvbuf = min_t(u64, tcp_space_from_win(sk, rcvwin), READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])); - if (rcvbuf > sk->sk_rcvbuf) { - WRITE_ONCE(sk->sk_rcvbuf, rcvbuf); + if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { + if (rcvbuf > sk->sk_rcvbuf) { + WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
- /* Make the window clamp follow along. */ - WRITE_ONCE(tp->window_clamp, - tcp_win_from_space(sk, rcvbuf)); + /* Make the window clamp follow along. */ + WRITE_ONCE(tp->window_clamp, + tcp_win_from_space(sk, rcvbuf)); + } + } else { + /* Make the window clamp follow along while being bounded + * by SO_RCVBUF. + */ + int clamp = tcp_win_from_space(sk, min(rcvbuf, sk->sk_rcvbuf)); + + if (clamp > tp->window_clamp) + WRITE_ONCE(tp->window_clamp, clamp); } } tp->rcvq_space.space = copied;