netdev - [PATCH net 5/6] tcp_metrics: annotate data-races around tm->tcpm

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Date: Wed,  2 Aug 2023 13:14:59 +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, 
	David Ahern <dsahern@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 5/6] tcp_metrics: annotate data-races around tm->tcpm_net

tm->tcpm_net can be read or written locklessly.

Instead of changing write_pnet() and read_pnet() and potentially
hurt performance, add the needed READ_ONCE()/WRITE_ONCE()
in tm_net() and tcpm_new().

Fixes: 849e8a0ca8d5 ("tcp_metrics: Add a field tcpm_net and verify it matches on lookup")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/tcp_metrics.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index fd4ab7a51cef210005146dfbc3235a2db717a44f..4fd274836a48f73d0b1206adfa14c17c3b28bc30 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -40,7 +40,7 @@ struct tcp_fastopen_metrics {
 
 struct tcp_metrics_block {
 	struct tcp_metrics_block __rcu	*tcpm_next;
-	possible_net_t			tcpm_net;
+	struct net			*tcpm_net;
 	struct inetpeer_addr		tcpm_saddr;
 	struct inetpeer_addr		tcpm_daddr;
 	unsigned long			tcpm_stamp;
@@ -51,9 +51,10 @@ struct tcp_metrics_block {
 	struct rcu_head			rcu_head;
 };
 
-static inline struct net *tm_net(struct tcp_metrics_block *tm)
+static inline struct net *tm_net(const struct tcp_metrics_block *tm)
 {
-	return read_pnet(&tm->tcpm_net);
+	/* Paired with the WRITE_ONCE() in tcpm_new() */
+	return READ_ONCE(tm->tcpm_net);
 }
 
 static bool tcp_metric_locked(struct tcp_metrics_block *tm,
@@ -197,7 +198,9 @@ static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,
 		if (!tm)
 			goto out_unlock;
 	}
-	write_pnet(&tm->tcpm_net, net);
+	/* Paired with the READ_ONCE() in tm_net() */
+	WRITE_ONCE(tm->tcpm_net, net);
+
 	tm->tcpm_saddr = *saddr;
 	tm->tcpm_daddr = *daddr;
 
-- 
2.41.0.640.ga95def55d0-goog