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Message-ID: <705dad54e6e6e9a010e571bf58e0b35a8ae70503.1701706073.git.pabeni@redhat.com>
Date: Mon, 4 Dec 2023 17:08:05 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: netdev@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>,
"David S. Miller" <davem@...emloft.net>,
David Ahern <dsahern@...nel.org>,
Jakub Kicinski <kuba@...nel.org>,
Neil Spring <ntspring@...com>,
David Gibson <david@...son.dropbear.id.au>,
Stefano Brivio <sbrivio@...hat.com>
Subject: [PATCH v2 net] tcp: fix mid stream window clamp.
After the blamed commit below, if the user-space application performs
window clamping when tp->rcv_wnd is 0, the TCP socket will never be
able to announce a non 0 receive window, even after completely emptying
the receive buffer and re-setting the window clamp to higher values.
Refactor tcp_set_window_clamp() to address the issue: when the user
decreases the current clamp value, set rcv_ssthresh according to the
same logic used at buffer initialization, but ensuring reserved mem
provisioning.
To avoid code duplication factor-out the relevant bits from
tcp_adjust_rcv_ssthresh() in a new helper and reuse it in the above
scenario.
When increasing the clamp value, give the rcv_ssthresh a chance to grow
according to previously implemented heuristic.
Fixes: 3aa7857fe1d7 ("tcp: enable mid stream window clamp")
Reported-by: David Gibson <david@...son.dropbear.id.au>
Reported-by: Stefano Brivio <sbrivio@...hat.com>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
v1 -> v2:
- respect SO_RESERVE_MEM provisioning (Eric)
---
include/net/tcp.h | 9 +++++++--
net/ipv4/tcp.c | 22 +++++++++++++++++++---
2 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index d2f0736b76b8..144ba48bb07b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1514,17 +1514,22 @@ static inline int tcp_full_space(const struct sock *sk)
return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
}
-static inline void tcp_adjust_rcv_ssthresh(struct sock *sk)
+static inline void __tcp_adjust_rcv_ssthresh(struct sock *sk, u32 new_ssthresh)
{
int unused_mem = sk_unused_reserved_mem(sk);
struct tcp_sock *tp = tcp_sk(sk);
- tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh, new_ssthresh);
if (unused_mem)
tp->rcv_ssthresh = max_t(u32, tp->rcv_ssthresh,
tcp_win_from_space(sk, unused_mem));
}
+static inline void tcp_adjust_rcv_ssthresh(struct sock *sk)
+{
+ __tcp_adjust_rcv_ssthresh(sk, 4U * tcp_sk(sk)->advmss);
+}
+
void tcp_cleanup_rbuf(struct sock *sk, int copied);
void __tcp_cleanup_rbuf(struct sock *sk, int copied);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 53bcc17c91e4..c9f078224569 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3368,9 +3368,25 @@ int tcp_set_window_clamp(struct sock *sk, int val)
return -EINVAL;
tp->window_clamp = 0;
} else {
- tp->window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
- SOCK_MIN_RCVBUF / 2 : val;
- tp->rcv_ssthresh = min(tp->rcv_wnd, tp->window_clamp);
+ u32 new_rcv_ssthresh, old_window_clamp = tp->window_clamp;
+ u32 new_window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
+ SOCK_MIN_RCVBUF / 2 : val;
+
+ if (new_window_clamp == old_window_clamp)
+ return 0;
+
+ tp->window_clamp = new_window_clamp;
+ if (new_window_clamp < old_window_clamp) {
+ /* need to apply the reserved mem provisioning only
+ * when shrinking the window clamp
+ */
+ __tcp_adjust_rcv_ssthresh(sk, tp->window_clamp);
+
+ } else {
+ new_rcv_ssthresh = min(tp->rcv_wnd, tp->window_clamp);
+ tp->rcv_ssthresh = max(new_rcv_ssthresh,
+ tp->rcv_ssthresh);
+ }
}
return 0;
}
--
2.42.0
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