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Commit 3a2bb84e authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net/packet: remove locking from packet_rcv_has_room() 



__packet_rcv_has_room() can now be run without lock being held.

po->pressure is only a non persistent hint, we can mark
all read/write accesses with READ_ONCE()/WRITE_ONCE()
to document the fact that the field could be written
without any synchronization.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2c51c627

net/packet/af_packet.c

+9 −11
Original line number Diff line number Diff line
@@ -1260,15 +1260,13 @@ 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 ret;

	bool has_room;

	int pressure, ret;



	spin_lock_bh(&po->sk.sk_receive_queue.lock);

	ret = __packet_rcv_has_room(po, skb);

	has_room = ret == ROOM_NORMAL;

	if (po->pressure == has_room)

		po->pressure = !has_room;

	spin_unlock_bh(&po->sk.sk_receive_queue.lock);

	pressure = ret != ROOM_NORMAL;



	if (READ_ONCE(po->pressure) != pressure)

		WRITE_ONCE(po->pressure, pressure);



	return ret;

}
@@ -1353,7 +1351,7 @@ 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(f->arr[i]);

		if (po_next != po_skip && !po_next->pressure &&

		if (po_next != po_skip && !READ_ONCE(po_next->pressure) &&

		    packet_rcv_has_room(po_next, skb) == ROOM_NORMAL) {

			if (i != j)

				po->rollover->sock = i;
@@ -3310,7 +3308,7 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, 
	if (skb == NULL)

		goto out;



	if (pkt_sk(sk)->pressure)

	if (READ_ONCE(pkt_sk(sk)->pressure))

		packet_rcv_has_room(pkt_sk(sk), NULL);



	if (pkt_sk(sk)->has_vnet_hdr) {
@@ -4129,8 +4127,8 @@ static __poll_t packet_poll(struct file *file, struct socket *sock, 
			TP_STATUS_KERNEL))

			mask |= EPOLLIN | EPOLLRDNORM;

	}

	if (po->pressure && __packet_rcv_has_room(po, NULL) == ROOM_NORMAL)

		po->pressure = 0;

	if (READ_ONCE(po->pressure) && __packet_rcv_has_room(po, NULL) == ROOM_NORMAL)

		WRITE_ONCE(po->pressure, 0);

	spin_unlock_bh(&sk->sk_receive_queue.lock);

	spin_lock_bh(&sk->sk_write_queue.lock);

	if (po->tx_ring.pg_vec) {