net/packet: convert po->tp_loss to an atomic flag

tp_loss can be read locklessly.

Convert it to an atomic flag to avoid races.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -2843,7 +2843,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 
 		if (unlikely(tp_len < 0)) {
 tpacket_error:
-			if (po->tp_loss) {
+			if (packet_sock_flag(po, PACKET_SOCK_TP_LOSS)) {
 				__packet_set_status(po, ph,
 						TP_STATUS_AVAILABLE);
 				packet_increment_head(&po->tx_ring);
@@ -3886,7 +3886,7 @@ packet_setsockopt(struct socket *sock, int level, int optname, sockptr_t optval,
 		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
 			ret = -EBUSY;
 		} else {
-			po->tp_loss = !!val;
+			packet_sock_flag_set(po, PACKET_SOCK_TP_LOSS, val);
 			ret = 0;
 		}
 		release_sock(sk);
@@ -4095,7 +4095,7 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
 		val = po->tp_reserve;
 		break;
 	case PACKET_LOSS:
-		val = po->tp_loss;
+		val = packet_sock_flag(po, PACKET_SOCK_TP_LOSS);
 		break;
 	case PACKET_TIMESTAMP:
 		val = READ_ONCE(po->tp_tstamp);

net/packet/diag.c

@@ -29,7 +29,7 @@ static int pdiag_put_info(const struct packet_sock *po, struct sk_buff *nlskb)
 		pinfo.pdi_flags |= PDI_ORIGDEV;
 	if (po->has_vnet_hdr)
 		pinfo.pdi_flags |= PDI_VNETHDR;
-	if (po->tp_loss)
+	if (packet_sock_flag(po, PACKET_SOCK_TP_LOSS))
 		pinfo.pdi_flags |= PDI_LOSS;
 
 	return nla_put(nlskb, PACKET_DIAG_INFO, sizeof(pinfo), &pinfo);

net/packet/internal.h

@@ -118,8 +118,7 @@ struct packet_sock {
 	struct mutex		pg_vec_lock;
 	unsigned long		flags;
 	unsigned int		running;	/* bind_lock must be held */
-	unsigned int		has_vnet_hdr:1, /* writer must hold sock lock */
-				tp_loss:1;
+	unsigned int		has_vnet_hdr:1; /* writer must hold sock lock */
 	int			pressure;
 	int			ifindex;	/* bound device		*/
 	__be16			num;
@@ -146,6 +145,7 @@ enum packet_sock_flags {
 	PACKET_SOCK_ORIGDEV,
 	PACKET_SOCK_AUXDATA,
 	PACKET_SOCK_TX_HAS_OFF,
+	PACKET_SOCK_TP_LOSS,
 };
 
 static inline void packet_sock_flag_set(struct packet_sock *po,