tcp_metrics: annotate data-races around tm->tcpm_lock

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>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230802131500.1478140-4-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 8386165..131fa30 100644 (file)
--- 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;