tcp_metrics: annotate data-races around tm->tcpm_vals[]

tm->tcpm_vals[] values can be read or written locklessly.

Add needed READ_ONCE()/WRITE_ONCE() to document this,
and force use of tcp_metric_get() and tcp_metric_set()

Fixes: 51c5d0c4 ("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>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_metrics.c

@@ -63,17 +63,19 @@ static bool tcp_metric_locked(struct tcp_metrics_block *tm,
 	return READ_ONCE(tm->tcpm_lock) & (1 << idx);
 }
 
-static u32 tcp_metric_get(struct tcp_metrics_block *tm,
+static u32 tcp_metric_get(const struct tcp_metrics_block *tm,
 			  enum tcp_metric_index idx)
 {
-	return tm->tcpm_vals[idx];
+	/* Paired with WRITE_ONCE() in tcp_metric_set() */
+	return READ_ONCE(tm->tcpm_vals[idx]);
 }
 
 static void tcp_metric_set(struct tcp_metrics_block *tm,
 			   enum tcp_metric_index idx,
 			   u32 val)
 {
-	tm->tcpm_vals[idx] = val;
+	/* Paired with READ_ONCE() in tcp_metric_get() */
+	WRITE_ONCE(tm->tcpm_vals[idx], val);
 }
 
 static bool addr_same(const struct inetpeer_addr *a,
@@ -115,13 +117,16 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm,
 	WRITE_ONCE(tm->tcpm_lock, val);
 
 	msval = dst_metric_raw(dst, RTAX_RTT);
-	tm->tcpm_vals[TCP_METRIC_RTT] = msval * USEC_PER_MSEC;
+	tcp_metric_set(tm, TCP_METRIC_RTT, msval * USEC_PER_MSEC);
 
 	msval = dst_metric_raw(dst, RTAX_RTTVAR);
-	tm->tcpm_vals[TCP_METRIC_RTTVAR] = msval * USEC_PER_MSEC;
-	tm->tcpm_vals[TCP_METRIC_SSTHRESH] = dst_metric_raw(dst, RTAX_SSTHRESH);
-	tm->tcpm_vals[TCP_METRIC_CWND] = dst_metric_raw(dst, RTAX_CWND);
-	tm->tcpm_vals[TCP_METRIC_REORDERING] = dst_metric_raw(dst, RTAX_REORDERING);
+	tcp_metric_set(tm, TCP_METRIC_RTTVAR, msval * USEC_PER_MSEC);
+	tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
+		       dst_metric_raw(dst, RTAX_SSTHRESH));
+	tcp_metric_set(tm, TCP_METRIC_CWND,
+		       dst_metric_raw(dst, RTAX_CWND));
+	tcp_metric_set(tm, TCP_METRIC_REORDERING,
+		       dst_metric_raw(dst, RTAX_REORDERING));
 	if (fastopen_clear) {
 		tm->tcpm_fastopen.mss = 0;
 		tm->tcpm_fastopen.syn_loss = 0;
@@ -667,7 +672,7 @@ static int tcp_metrics_fill_info(struct sk_buff *msg,
 		if (!nest)
 			goto nla_put_failure;
 		for (i = 0; i < TCP_METRIC_MAX_KERNEL + 1; i++) {
-			u32 val = tm->tcpm_vals[i];
+			u32 val = tcp_metric_get(tm, i);
 
 			if (!val)
 				continue;