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@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230802131500.1478140-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index fd4ab7a..4fd2748 100644 (file)
--- 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;