netdev - [PATCH net 03/11] tcp: annotate data-races around tp->keepalive

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Date: Wed, 19 Jul 2023 21:28:49 +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 03/11] tcp: annotate data-races around tp->keepalive_time

do_tcp_getsockopt() reads tp->keepalive_time while another cpu
might change its value.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/tcp.h | 7 +++++--
 net/ipv4/tcp.c    | 3 ++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index efaed11e691d52db0fcece85d966954763d3cfcf..ff7372410472246d372402dfdfd6391544be8259 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1515,9 +1515,12 @@ static inline int keepalive_intvl_when(const struct tcp_sock *tp)
 static inline int keepalive_time_when(const struct tcp_sock *tp)
 {
 	struct net *net = sock_net((struct sock *)tp);
+	int val;
 
-	return tp->keepalive_time ? :
-		READ_ONCE(net->ipv4.sysctl_tcp_keepalive_time);
+	/* Paired with WRITE_ONCE() in tcp_sock_set_keepidle_locked() */
+	val = READ_ONCE(tp->keepalive_time);
+
+	return val ? : READ_ONCE(net->ipv4.sysctl_tcp_keepalive_time);
 }
 
 static inline int keepalive_probes(const struct tcp_sock *tp)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 03ae6554c78d1e42894a8e511cef362134660aac..b4f7856dfb1611f02073699ee24d48f1a6fe7b87 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3312,7 +3312,8 @@ int tcp_sock_set_keepidle_locked(struct sock *sk, int val)
 	if (val < 1 || val > MAX_TCP_KEEPIDLE)
 		return -EINVAL;
 
-	tp->keepalive_time = val * HZ;
+	/* Paired with WRITE_ONCE() in keepalive_time_when() */
+	WRITE_ONCE(tp->keepalive_time, val * HZ);
 	if (sock_flag(sk, SOCK_KEEPOPEN) &&
 	    !((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))) {
 		u32 elapsed = keepalive_time_elapsed(tp);
-- 
2.41.0.255.g8b1d071c50-goog