From: Wesley Atwell <redacted>

Teach TCP to grow sk_rcvbuf when scale rounding would otherwise expose
more sender-visible window than the current hard receive-memory backing
can cover.

The new helper keeps backlog and memory-pressure limits in the same
units as the rest of the receive path, while __tcp_select_window()
backs any rounding slack before advertising it.

Signed-off-by: Wesley Atwell <redacted>
---
 include/net/tcp.h     | 12 ++++++++++++
 net/ipv4/tcp_input.c  | 36 ++++++++++++++++++++++++++++++++++--
 net/ipv4/tcp_output.c | 15 +++++++++++++--
 3 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index fc22ab6b80d5..5b479ad44f89 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -397,6 +397,7 @@ int tcp_ioctl(struct sock *sk, int cmd, int *karg);
 enum skb_drop_reason tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb);
 void tcp_rcvbuf_grow(struct sock *sk, u32 newval);
+bool tcp_try_grow_rcvbuf(struct sock *sk, int needed);
 void tcp_rcv_space_adjust(struct sock *sk);
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
 void tcp_twsk_destructor(struct sock *sk);

@@ -1844,6 +1845,17 @@ static inline int tcp_rwnd_avail(const struct sock *sk)
 	return tcp_rmem_avail(sk) - READ_ONCE(sk->sk_backlog.len);
 }
 
+/* Passive children clone the listener's sk_socket until accept() grafts
+ * their own struct socket,