Patch "tcp: annotate data-races around fastopenq.max_qlen" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tcp: annotate data-races around fastopenq.max_qlen

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-annotate-data-races-around-fastopenq.max_qlen.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5b09a1d0f89f0fe1f11380b4827375463adc9b58
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Wed Jul 19 21:28:57 2023 +0000

    tcp: annotate data-races around fastopenq.max_qlen
    
    [ Upstream commit 70f360dd7042cb843635ece9d28335a4addff9eb ]
    
    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@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230719212857.3943972-12-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index b4c08ac869835..91a37c99ba665 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 c9b955d9d7ace..79f29e138fc9f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4254,7 +4254,7 @@ 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 45cc7f1ca2961..85e4953f11821 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;