netdev - [PATCH v2 net-next 8/8] tcp: reclaim 8 bytes in struct request_sock

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Message-ID: <20250919204856.2977245-9-edumazet@google.com>
Date: Fri, 19 Sep 2025 20:48:56 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Neal Cardwell <ncardwell@...gle.com>, 
	Willem de Bruijn <willemb@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v2 net-next 8/8] tcp: reclaim 8 bytes in struct request_sock_queue

synflood_warned had to be u32 for xchg(), but ensuring
atomicity is not really needed.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/request_sock.h | 2 +-
 net/ipv4/tcp_input.c       | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 6a5ec1418e8552b4aa9d25d61afa5376187b569d..cd4d4cf71d0d22bdb980f6e1cbe10e8307965b0e 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -185,8 +185,8 @@ struct fastopen_queue {
 struct request_sock_queue {
 	spinlock_t		rskq_lock;
 	u8			rskq_defer_accept;
+	u8			synflood_warned;
 
-	u32			synflood_warned;
 	atomic_t		qlen;
 	atomic_t		young;
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f93d48d98d5dacf2ee868cd6b2d65a396443d106..79d5252ed6cc1a24ec898f4168d47c39c6e92fe1 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -7282,8 +7282,8 @@ static bool tcp_syn_flood_action(struct sock *sk, const char *proto)
 #endif
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
 
-	if (!READ_ONCE(queue->synflood_warned) && syncookies != 2 &&
-	    xchg(&queue->synflood_warned, 1) == 0) {
+	if (syncookies != 2 && !READ_ONCE(queue->synflood_warned)) {
+		WRITE_ONCE(queue->synflood_warned, 1);
 		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
 			net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
 					proto, inet6_rcv_saddr(sk),
-- 
2.51.0.470.ga7dc726c21-goog