tcp: annotate races around tp->urg_data

tcp_poll() and tcp_ioctl() are reading tp->urg_data without socket lock
owned.

Also, it is faster to first check tp->urg_data in tcp_poll(),
then tp->urg_seq == tp->copied_seq, because tp->urg_seq is
located in a different/cold cache line.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -545,10 +545,11 @@ __poll_t tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
 	if (state != TCP_SYN_SENT &&
 	    (state != TCP_SYN_RECV || rcu_access_pointer(tp->fastopen_rsk))) {
 		int target = sock_rcvlowat(sk, 0, INT_MAX);
+		u16 urg_data = READ_ONCE(tp->urg_data);
 
-		if (READ_ONCE(tp->urg_seq) == READ_ONCE(tp->copied_seq) &&
-		    !sock_flag(sk, SOCK_URGINLINE) &&
-		    tp->urg_data)
+		if (urg_data &&
+		    READ_ONCE(tp->urg_seq) == READ_ONCE(tp->copied_seq) &&
+		    !sock_flag(sk, SOCK_URGINLINE))
 			target++;
 
 		if (tcp_stream_is_readable(sk, target))
@@ -573,7 +574,7 @@ __poll_t tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
 		} else
 			mask |= EPOLLOUT | EPOLLWRNORM;
 
-		if (tp->urg_data & TCP_URG_VALID)
+		if (urg_data & TCP_URG_VALID)
 			mask |= EPOLLPRI;
 	} else if (state == TCP_SYN_SENT && inet_sk(sk)->defer_connect) {
 		/* Active TCP fastopen socket with defer_connect
@@ -607,7 +608,7 @@ int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 		unlock_sock_fast(sk, slow);
 		break;
 	case SIOCATMARK:
-		answ = tp->urg_data &&
+		answ = READ_ONCE(tp->urg_data) &&
 		       READ_ONCE(tp->urg_seq) == READ_ONCE(tp->copied_seq);
 		break;
 	case SIOCOUTQ:
@@ -1465,7 +1466,7 @@ static int tcp_recv_urg(struct sock *sk, struct msghdr *msg, int len, int flags)
 		char c = tp->urg_data;
 
 		if (!(flags & MSG_PEEK))
-			tp->urg_data = TCP_URG_READ;
+			WRITE_ONCE(tp->urg_data, TCP_URG_READ);
 
 		/* Read urgent data. */
 		msg->msg_flags |= MSG_OOB;
@@ -2465,7 +2466,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len,
 
 skip_copy:
 		if (tp->urg_data && after(tp->copied_seq, tp->urg_seq)) {
-			tp->urg_data = 0;
+			WRITE_ONCE(tp->urg_data, 0);
 			tcp_fast_path_check(sk);
 		}
 
@@ -2959,7 +2960,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tcp_clear_xmit_timers(sk);
 	__skb_queue_purge(&sk->sk_receive_queue);
 	WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
-	tp->urg_data = 0;
+	WRITE_ONCE(tp->urg_data, 0);
 	tcp_write_queue_purge(sk);
 	tcp_fastopen_active_disable_ofo_check(sk);
 	skb_rbtree_purge(&tp->out_of_order_queue);

net/ipv4/tcp_input.c

@@ -5591,7 +5591,7 @@ static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
 		}
 	}
 
-	tp->urg_data = TCP_URG_NOTYET;
+	WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
 	WRITE_ONCE(tp->urg_seq, ptr);
 
 	/* Disable header prediction. */
@@ -5617,7 +5617,7 @@ static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *t
 			u8 tmp;
 			if (skb_copy_bits(skb, ptr, &tmp, 1))
 				BUG();
-			tp->urg_data = TCP_URG_VALID | tmp;
+			WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
 			if (!sock_flag(sk, SOCK_DEAD))
 				sk->sk_data_ready(sk);
 		}