netdev - [PATCH net-next 6/6] tcp: set TCP_DEFER

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Date: Fri,  4 Aug 2023 14:46:16 +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: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 6/6] tcp: set TCP_DEFER_ACCEPT locklessly

rskq_defer_accept field can be read/written without
the need of holding the socket lock.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/tcp.c           | 13 ++++++-------
 net/ipv4/tcp_input.c     |  2 +-
 net/ipv4/tcp_minisocks.c |  2 +-
 3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5c71b4fe11d1c34456976d60eb8742641111dd62..4fbc7ff8c53c05cbef3d108527239c7ec8c1363e 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3479,6 +3479,12 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		else
 			WRITE_ONCE(tp->linger2, val * HZ);
 		return 0;
+	case TCP_DEFER_ACCEPT:
+		/* Translate value in seconds to number of retransmits */
+		WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,
+			   secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
+					   TCP_RTO_MAX / HZ));
+		return 0;
 	}
 
 	sockopt_lock_sock(sk);
@@ -3584,13 +3590,6 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 			tp->save_syn = val;
 		break;
 
-	case TCP_DEFER_ACCEPT:
-		/* Translate value in seconds to number of retransmits */
-		WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,
-			   secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
-					   TCP_RTO_MAX / HZ));
-		break;
-
 	case TCP_WINDOW_CLAMP:
 		err = tcp_set_window_clamp(sk, val);
 		break;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f445f5a7c0ebf5f7ab2b2402357f3749d954c0e8..972c3b16369589293eb15febe52e72d5c596b032 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6325,7 +6325,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 		if (fastopen_fail)
 			return -1;
 		if (sk->sk_write_pending ||
-		    icsk->icsk_accept_queue.rskq_defer_accept ||
+		    READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept) ||
 		    inet_csk_in_pingpong_mode(sk)) {
 			/* Save one ACK. Data will be ready after
 			 * several ticks, if write_pending is set.
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index c8f2aa0033871ed3f8b6b045c2cbca6e88bf2b61..32a70e3530db3247986ab5cb08c8a46babf86ad6 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -794,7 +794,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 		return sk;
 
 	/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
-	if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
+	if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) &&
 	    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
 		inet_rsk(req)->acked = 1;
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
-- 
2.41.0.640.ga95def55d0-goog