CAPI: Rework capiminor RX handler

Avoid re-queuing skbs unless the error detected in handle_recv_skb is
expected to be recoverable such as lacking memory, a full CAPI queue, a
full TTY input buffer, or a not yet existing TTY.
Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/capi/capi.c

@@ -436,15 +436,13 @@ gen_data_b3_resp_for(struct capiminor *mp, struct sk_buff *skb)
 
 static int handle_recv_skb(struct capiminor *mp, struct sk_buff *skb)
 {
+	unsigned int datalen = skb->len - CAPIMSG_LEN(skb->data);
 	struct tty_struct *tty;
 	struct sk_buff *nskb;
-	int datalen;
 	u16 errcode, datahandle;
 	struct tty_ldisc *ld;
 	int ret = -1;
 
-	datalen = skb->len - CAPIMSG_LEN(skb->data);
-
 	tty = tty_port_tty_get(&mp->port);
 	if (!tty) {
 #ifdef _DEBUG_DATAFLOW
@@ -454,50 +452,68 @@ static int handle_recv_skb(struct capiminor *mp, struct sk_buff *skb)
 	}
 	
 	ld = tty_ldisc_ref(tty);
-	if (!ld)
-		goto out1;
+	if (!ld) {
+		/* fatal error, do not requeue */
+		ret = 0;
+		kfree_skb(skb);
+		goto deref_tty;
+	}
 
 	if (ld->ops->receive_buf == NULL) {
 #if defined(_DEBUG_DATAFLOW) || defined(_DEBUG_TTYFUNCS)
 		printk(KERN_DEBUG "capi: ldisc has no receive_buf function\n");
 #endif
-		goto out2;
+		/* fatal error, do not requeue */
+		goto free_skb;
 	}
 	if (mp->ttyinstop) {
 #if defined(_DEBUG_DATAFLOW) || defined(_DEBUG_TTYFUNCS)
 		printk(KERN_DEBUG "capi: recv tty throttled\n");
 #endif
-		goto out2;
+		goto deref_ldisc;
 	}
+
 	if (tty->receive_room < datalen) {
 #if defined(_DEBUG_DATAFLOW) || defined(_DEBUG_TTYFUNCS)
 		printk(KERN_DEBUG "capi: no room in tty\n");
 #endif
-		goto out2;
+		goto deref_ldisc;
 	}
-	if ((nskb = gen_data_b3_resp_for(mp, skb)) == NULL) {
+
+	nskb = gen_data_b3_resp_for(mp, skb);
+	if (!nskb) {
 		printk(KERN_ERR "capi: gen_data_b3_resp failed\n");
-		goto out2;
+		goto deref_ldisc;
 	}
-	datahandle = CAPIMSG_U16(skb->data,CAPIMSG_BASELEN+4);
+
+	datahandle = CAPIMSG_U16(skb->data, CAPIMSG_BASELEN + 4);
+
 	errcode = capi20_put_message(mp->ap, nskb);
-	if (errcode != CAPI_NOERROR) {
+
+	if (errcode == CAPI_NOERROR) {
+		skb_pull(skb, CAPIMSG_LEN(skb->data));
+#ifdef _DEBUG_DATAFLOW
+		printk(KERN_DEBUG "capi: DATA_B3_RESP %u len=%d => ldisc\n",
+					datahandle, skb->len);
+#endif
+		ld->ops->receive_buf(tty, skb->data, NULL, skb->len);
+	} else {
 		printk(KERN_ERR "capi: send DATA_B3_RESP failed=%x\n",
 				errcode);
 		kfree_skb(nskb);
-		goto out2;
+
+		if (errcode == CAPI_SENDQUEUEFULL)
+			goto deref_ldisc;
 	}
-	(void)skb_pull(skb, CAPIMSG_LEN(skb->data));
-#ifdef _DEBUG_DATAFLOW
-	printk(KERN_DEBUG "capi: DATA_B3_RESP %u len=%d => ldisc\n",
-				datahandle, skb->len);
-#endif
-	ld->ops->receive_buf(tty, skb->data, NULL, skb->len);
-	kfree_skb(skb);
+
+free_skb:
 	ret = 0;
-out2:
+	kfree_skb(skb);
+
+deref_ldisc:
 	tty_ldisc_deref(ld);
-out1:
+
+deref_tty:
 	tty_kref_put(tty);
 	return ret;
 }