[PATCH net 3/6] tcp_metrics: annotate data-races around tm->tcpm_lock

From: Eric Dumazet <edumazet@google.com>
To: "David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	 Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com,
	 David Ahern <dsahern@kernel.org>,
	Kuniyuki Iwashima <kuniyu@amazon.com>,
	 Eric Dumazet <edumazet@google.com>
Subject: [PATCH net 3/6] tcp_metrics: annotate data-races around tm->tcpm_lock
Date: Wed,  2 Aug 2023 13:14:57 +0000	[thread overview]
Message-ID: <20230802131500.1478140-4-edumazet@google.com> (raw)
In-Reply-To: <20230802131500.1478140-1-edumazet@google.com>

tm->tcpm_lock can be read or written locklessly.

Add needed READ_ONCE()/WRITE_ONCE() to document this.

Fixes: 51c5d0c4b169 ("tcp: Maintain dynamic metrics in local cache.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp_metrics.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 83861658879638149d2746290a285a4f75fc3117..131fa300496914f78c682182f0db480ceb71b6a0 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -59,7 +59,8 @@ static inline struct net *tm_net(struct tcp_metrics_block *tm)
 static bool tcp_metric_locked(struct tcp_metrics_block *tm,
 			      enum tcp_metric_index idx)
 {
-	return tm->tcpm_lock & (1 << idx);
+	/* Paired with WRITE_ONCE() in tcpm_suck_dst() */
+	return READ_ONCE(tm->tcpm_lock) & (1 << idx);
 }
 
 static u32 tcp_metric_get(struct tcp_metrics_block *tm,
@@ -110,7 +111,8 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm,
 		val |= 1 << TCP_METRIC_CWND;
 	if (dst_metric_locked(dst, RTAX_REORDERING))
 		val |= 1 << TCP_METRIC_REORDERING;
-	tm->tcpm_lock = val;
+	/* Paired with READ_ONCE() in tcp_metric_locked() */
+	WRITE_ONCE(tm->tcpm_lock, val);
 
 	msval = dst_metric_raw(dst, RTAX_RTT);
 	tm->tcpm_vals[TCP_METRIC_RTT] = msval * USEC_PER_MSEC;
-- 
2.41.0.640.ga95def55d0-goog

