netdev - [PATCH net 11/11] tcp: annotate data-races around fastopenq.max

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Date: Wed, 19 Jul 2023 21:28:57 +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, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 11/11] tcp: annotate data-races around fastopenq.max_qlen

This field can be read locklessly.

Fixes: 1536e2857bd3 ("tcp: Add a TCP_FASTOPEN socket option to get a max backlog on its listner")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/tcp.h     | 2 +-
 net/ipv4/tcp.c          | 2 +-
 net/ipv4/tcp_fastopen.c | 6 ++++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index b4c08ac86983568a9511258708724da15d0b999e..91a37c99ba6651c075d1547c5545700be3e5593c 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -513,7 +513,7 @@ static inline void fastopen_queue_tune(struct sock *sk, int backlog)
 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
 	int somaxconn = READ_ONCE(sock_net(sk)->core.sysctl_somaxconn);
 
-	queue->fastopenq.max_qlen = min_t(unsigned int, backlog, somaxconn);
+	WRITE_ONCE(queue->fastopenq.max_qlen, min_t(unsigned int, backlog, somaxconn));
 }
 
 static inline void tcp_move_syn(struct tcp_sock *tp,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3e137e9a18f552a02d8c74e1af34ba2356e4d8ed..8ed52e1e3c99a334a47964d8fd05c720a8f683f9 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4145,7 +4145,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
 		break;
 
 	case TCP_FASTOPEN:
-		val = icsk->icsk_accept_queue.fastopenq.max_qlen;
+		val = READ_ONCE(icsk->icsk_accept_queue.fastopenq.max_qlen);
 		break;
 
 	case TCP_FASTOPEN_CONNECT:
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 45cc7f1ca29618e3ac1066cb49e7d6dc90e1c64d..85e4953f118215ba7100931dccb37ad871c5dfd2 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -296,6 +296,7 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
 static bool tcp_fastopen_queue_check(struct sock *sk)
 {
 	struct fastopen_queue *fastopenq;
+	int max_qlen;
 
 	/* Make sure the listener has enabled fastopen, and we don't
 	 * exceed the max # of pending TFO requests allowed before trying
@@ -308,10 +309,11 @@ static bool tcp_fastopen_queue_check(struct sock *sk)
 	 * temporarily vs a server not supporting Fast Open at all.
 	 */
 	fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
-	if (fastopenq->max_qlen == 0)
+	max_qlen = READ_ONCE(fastopenq->max_qlen);
+	if (max_qlen == 0)
 		return false;
 
-	if (fastopenq->qlen >= fastopenq->max_qlen) {
+	if (fastopenq->qlen >= max_qlen) {
 		struct request_sock *req1;
 		spin_lock(&fastopenq->lock);
 		req1 = fastopenq->rskq_rst_head;
-- 
2.41.0.255.g8b1d071c50-goog