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

Not only this removes some READ_ONCE()/WRITE_ONCE(),
this also removes one integer.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -1307,22 +1307,23 @@ static int __packet_rcv_has_room(const struct packet_sock *po,
 
 static int packet_rcv_has_room(struct packet_sock *po, struct sk_buff *skb)
 {
-	int pressure, ret;
+	bool pressure;
+	int ret;
 
 	ret = __packet_rcv_has_room(po, skb);
 	pressure = ret != ROOM_NORMAL;
 
-	if (READ_ONCE(po->pressure) != pressure)
-		WRITE_ONCE(po->pressure, pressure);
+	if (packet_sock_flag(po, PACKET_SOCK_PRESSURE) != pressure)
+		packet_sock_flag_set(po, PACKET_SOCK_PRESSURE, pressure);
 
 	return ret;
 }
 
 static void packet_rcv_try_clear_pressure(struct packet_sock *po)
 {
-	if (READ_ONCE(po->pressure) &&
+	if (packet_sock_flag(po, PACKET_SOCK_PRESSURE) &&
 	    __packet_rcv_has_room(po, NULL) == ROOM_NORMAL)
-		WRITE_ONCE(po->pressure,  0);
+		packet_sock_flag_set(po, PACKET_SOCK_PRESSURE, false);
 }
 
 static void packet_sock_destruct(struct sock *sk)
@@ -1409,7 +1410,8 @@ static unsigned int fanout_demux_rollover(struct packet_fanout *f,
 	i = j = min_t(int, po->rollover->sock, num - 1);
 	do {
 		po_next = pkt_sk(rcu_dereference(f->arr[i]));
-		if (po_next != po_skip && !READ_ONCE(po_next->pressure) &&
+		if (po_next != po_skip &&
+		    !packet_sock_flag(po_next, PACKET_SOCK_PRESSURE) &&
 		    packet_rcv_has_room(po_next, skb) == ROOM_NORMAL) {
 			if (i != j)
 				po->rollover->sock = i;

net/packet/internal.h

@@ -117,7 +117,6 @@ struct packet_sock {
 	spinlock_t		bind_lock;
 	struct mutex		pg_vec_lock;
 	unsigned long		flags;
-	int			pressure;
 	int			ifindex;	/* bound device		*/
 	__be16			num;
 	struct packet_rollover	*rollover;
@@ -146,6 +145,7 @@ enum packet_sock_flags {
 	PACKET_SOCK_TP_LOSS,
 	PACKET_SOCK_HAS_VNET_HDR,
 	PACKET_SOCK_RUNNING,
+	PACKET_SOCK_PRESSURE,
 };
 
 static inline void packet_sock_flag_set(struct packet_sock *po,