net: annotate data-races around sk->sk_max_pacing_rate

sk_getsockopt() runs locklessly. This means sk->sk_max_pacing_rate
can be read while other threads are changing its value.

Fixes: 62748f32 ("net: introduce SO_MAX_PACING_RATE")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -1439,7 +1439,8 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 			cmpxchg(&sk->sk_pacing_status,
 				SK_PACING_NONE,
 				SK_PACING_NEEDED);
-		sk->sk_max_pacing_rate = ulval;
+		/* Pairs with READ_ONCE() from sk_getsockopt() */
+		WRITE_ONCE(sk->sk_max_pacing_rate, ulval);
 		sk->sk_pacing_rate = min(sk->sk_pacing_rate, ulval);
 		break;
 		}
@@ -1903,12 +1904,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 #endif
 
 	case SO_MAX_PACING_RATE:
+		/* The READ_ONCE() pair with the WRITE_ONCE() in sk_setsockopt() */
 		if (sizeof(v.ulval) != sizeof(v.val) && len >= sizeof(v.ulval)) {
 			lv = sizeof(v.ulval);
-			v.ulval = sk->sk_max_pacing_rate;
+			v.ulval = READ_ONCE(sk->sk_max_pacing_rate);
 		} else {
 			/* 32bit version */
-			v.val = min_t(unsigned long, sk->sk_max_pacing_rate, ~0U);
+			v.val = min_t(unsigned long, ~0U,
+				      READ_ONCE(sk->sk_max_pacing_rate));
 		}
 		break;