net/af_iucv: count packets in the xmit path

The TX code keeps track of all skbs that are in-flight but haven't
actually been sent out yet. For native IUCV sockets that's not a huge
deal, but with TRANS_HIPER sockets it would be much better if we
didn't need to maintain a list of skb clones.

Note that we actually only care about the _count_ of skbs in this stage
of the TX pipeline. So as prep work for removing the skb tracking on
TRANS_HIPER sockets, keep track of the skb count in a separate variable
and pair any list {enqueue, unlink} with a count {increment, decrement}.

Then replace all occurences where we currently look at the skb list's
fill level.

Signed-off-by: Julian Wiedmann <[e-mail]>
Acked-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/iucv/af_iucv.h

···
 	u8			flags;
 	u16			msglimit;
 	u16			msglimit_peer;
+	atomic_t		skbs_in_xmit;
 	atomic_t		msg_sent;
 	atomic_t		msg_recv;
 	atomic_t		pendings;

net/iucv/af_iucv.c

···
 	if (sk->sk_state != IUCV_CONNECTED)
 		return 1;
 	if (iucv->transport == AF_IUCV_TRANS_IUCV)
-		return (skb_queue_len(&iucv->send_skb_q) < iucv->path->msglim);
+		return (atomic_read(&iucv->skbs_in_xmit) < iucv->path->msglim);
 	else
 		return ((atomic_read(&iucv->msg_sent) < iucv->msglimit_peer) &&
 			(atomic_read(&iucv->pendings) <= 0));
···
 	}
 
 	skb_queue_tail(&iucv->send_skb_q, nskb);
+	atomic_inc(&iucv->skbs_in_xmit);
 	err = dev_queue_xmit(skb);
 	if (net_xmit_eval(err)) {
+		atomic_dec(&iucv->skbs_in_xmit);
 		skb_unlink(nskb, &iucv->send_skb_q);
 		kfree_skb(nskb);
 	} else {
···
 		sk->sk_state = IUCV_CLOSING;
 		sk->sk_state_change(sk);
 
-		if (!err && !skb_queue_empty(&iucv->send_skb_q)) {
+		if (!err && atomic_read(&iucv->skbs_in_xmit) > 0) {
 			if (sock_flag(sk, SOCK_LINGER) && sk->sk_lingertime)
 				timeo = sk->sk_lingertime;
 			else
···
 	atomic_set(&iucv->pendings, 0);
 	iucv->flags = 0;
 	iucv->msglimit = 0;
+	atomic_set(&iucv->skbs_in_xmit, 0);
 	atomic_set(&iucv->msg_sent, 0);
 	atomic_set(&iucv->msg_recv, 0);
 	iucv->path = NULL;
···
 		}
 	} else { /* Classic VM IUCV transport */
 		skb_queue_tail(&iucv->send_skb_q, skb);
+		atomic_inc(&iucv->skbs_in_xmit);
 
 		if (((iucv->path->flags & IUCV_IPRMDATA) & iucv->flags) &&
 		    skb->len <= 7) {
···
 			/* on success: there is no message_complete callback */
 			/* for an IPRMDATA msg; remove skb from send queue   */
 			if (err == 0) {
+				atomic_dec(&iucv->skbs_in_xmit);
 				skb_unlink(skb, &iucv->send_skb_q);
 				kfree_skb(skb);
 			}
···
 			/* IUCV_IPRMDATA path flag is set... sever path */
 			if (err == 0x15) {
 				pr_iucv->path_sever(iucv->path, NULL);
+				atomic_dec(&iucv->skbs_in_xmit);
 				skb_unlink(skb, &iucv->send_skb_q);
 				err = -EPIPE;
 				goto fail;
···
 			} else {
 				err = -EPIPE;
 			}
+
+			atomic_dec(&iucv->skbs_in_xmit);
 			skb_unlink(skb, &iucv->send_skb_q);
 			goto fail;
 		}
···
 {
 	struct sock *sk = path->private;
 	struct sk_buff *this = NULL;
-	struct sk_buff_head *list = &iucv_sk(sk)->send_skb_q;
+	struct sk_buff_head *list;
 	struct sk_buff *list_skb;
+	struct iucv_sock *iucv;
 	unsigned long flags;
+
+	iucv = iucv_sk(sk);
+	list = &iucv->send_skb_q;
 
 	bh_lock_sock(sk);
 
···
 			break;
 		}
 	}
-	if (this)
+	if (this) {
+		atomic_dec(&iucv->skbs_in_xmit);
 		__skb_unlink(this, list);
+	}
+
 	spin_unlock_irqrestore(&list->lock, flags);
 
 	if (this) {
···
 	}
 
 	if (sk->sk_state == IUCV_CLOSING) {
-		if (skb_queue_empty(&iucv_sk(sk)->send_skb_q)) {
+		if (atomic_read(&iucv->skbs_in_xmit) == 0) {
 			sk->sk_state = IUCV_CLOSED;
 			sk->sk_state_change(sk);
 		}
···
 		if (skb_shinfo(list_skb) == skb_shinfo(skb)) {
 			switch (n) {
 			case TX_NOTIFY_OK:
+				atomic_dec(&iucv->skbs_in_xmit);
 				__skb_unlink(list_skb, list);
 				kfree_skb(list_skb);
 				iucv_sock_wake_msglim(sk);
···
 				atomic_inc(&iucv->pendings);
 				break;
 			case TX_NOTIFY_DELAYED_OK:
+				atomic_dec(&iucv->skbs_in_xmit);
 				__skb_unlink(list_skb, list);
 				atomic_dec(&iucv->pendings);
 				if (atomic_read(&iucv->pendings) <= 0)
···
 			case TX_NOTIFY_TPQFULL: /* not yet used */
 			case TX_NOTIFY_GENERALERROR:
 			case TX_NOTIFY_DELAYED_GENERALERROR:
+				atomic_dec(&iucv->skbs_in_xmit);
 				__skb_unlink(list_skb, list);
 				kfree_skb(list_skb);
 				if (sk->sk_state == IUCV_CONNECTED) {
···
 	spin_unlock_irqrestore(&list->lock, flags);
 
 	if (sk->sk_state == IUCV_CLOSING) {
-		if (skb_queue_empty(&iucv_sk(sk)->send_skb_q)) {
+		if (atomic_read(&iucv->skbs_in_xmit) == 0) {
 			sk->sk_state = IUCV_CLOSED;
 			sk->sk_state_change(sk);
 		}