net: annotate data-races around sk->sk_reserved_mem

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

Add missing annotations where they are needed.

Fixes: 2bb2f5f ("net: add new socket option SO_RESERVE_MEM")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -1007,7 +1007,7 @@ static void sock_release_reserved_memory(struct sock *sk, int bytes)
 	bytes = round_down(bytes, PAGE_SIZE);
 
 	WARN_ON(bytes > sk->sk_reserved_mem);
-	sk->sk_reserved_mem -= bytes;
+	WRITE_ONCE(sk->sk_reserved_mem, sk->sk_reserved_mem - bytes);
 	sk_mem_reclaim(sk);
 }
 
@@ -1044,7 +1044,8 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 	}
 	sk->sk_forward_alloc += pages << PAGE_SHIFT;
 
-	sk->sk_reserved_mem += pages << PAGE_SHIFT;
+	WRITE_ONCE(sk->sk_reserved_mem,
+		   sk->sk_reserved_mem + (pages << PAGE_SHIFT));
 
 	return 0;
 }
@@ -1973,7 +1974,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case SO_RESERVE_MEM:
-		v.val = sk->sk_reserved_mem;
+		v.val = READ_ONCE(sk->sk_reserved_mem);
 		break;
 
 	case SO_TXREHASH: