diff options
| author | Eric Dumazet <edumazet@google.com> | 2025-10-03 18:41:19 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2025-10-06 13:08:48 -0700 |
| commit | 21b29e74ffe5a6c851c235bb80bf5ee26292c67b (patch) | |
| tree | acaf3c0e18ef261259cdc2f3893c5dc798ceab91 /net/ipv4/tcp.c | |
| parent | 95920c2ed02bde551ab654e9749c2ca7bc3100e0 (diff) | |
tcp: take care of zero tp->window_clamp in tcp_set_rcvlowat()
Some applications (like selftests/net/tcp_mmap.c) call SO_RCVLOWAT
on their listener, before accept().
This has an unfortunate effect on wscale selection in
tcp_select_initial_window() during 3WHS.
For instance, tcp_mmap was negotiating wscale 4, regardless
of tcp_rmem[2] and sysctl_rmem_max.
Do not change tp->window_clamp if it is zero
or bigger than our computed value.
Zero value is special, it allows tcp_select_initial_window()
to enable autotuning.
Note that SO_RCVLOWAT use on listener is probably not wise,
because tp->scaling_ratio has a default value, possibly wrong.
Fixes: d1361840f8c5 ("tcp: fix SO_RCVLOWAT and RCVBUF autotuning")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20251003184119.2526655-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv4/tcp.c')
| -rw-r--r-- | net/ipv4/tcp.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 7949d16506a4..8a18aeca7ab0 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1791,6 +1791,7 @@ EXPORT_IPV6_MOD(tcp_peek_len); /* Make sure sk_rcvbuf is big enough to satisfy SO_RCVLOWAT hint */ int tcp_set_rcvlowat(struct sock *sk, int val) { + struct tcp_sock *tp = tcp_sk(sk); int space, cap; if (sk->sk_userlocks & SOCK_RCVBUF_LOCK) @@ -1809,7 +1810,9 @@ int tcp_set_rcvlowat(struct sock *sk, int val) space = tcp_space_from_win(sk, val); if (space > sk->sk_rcvbuf) { WRITE_ONCE(sk->sk_rcvbuf, space); - WRITE_ONCE(tcp_sk(sk)->window_clamp, val); + + if (tp->window_clamp && tp->window_clamp < val) + WRITE_ONCE(tp->window_clamp, val); } return 0; } |