net: annotate lockless accesses to sk->sk_ack_backlog

sk->sk_ack_backlog can be read without any lock being held.
We need to use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing
and/or potential KCSAN warnings.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/em_meta.c b/net/sched/em_meta.c
index 3177dcb1..ebb6e243 100644
--- a/net/sched/em_meta.c
+++ b/net/sched/em_meta.c
@@ -521,7 +521,7 @@ META_COLLECTOR(int_sk_ack_bl)
 		*err = -1;
 		return;
 	}
-	dst->value = sk->sk_ack_backlog;
+	dst->value = READ_ONCE(sk->sk_ack_backlog);
 }
 
 META_COLLECTOR(int_sk_max_ack_bl)