[PATCH] ppp_synctty.c receive/write_wakeup fix

Allow receive and write_wakeup callbacks to be called at hard interrupt
context and/or with interrupts disabled (removes softirq warning).

This mirrors changes by Paul Mackerras to ppp_async.c for the same purpose.
Patch has been previously posted for comments and has been tested with
success by multiple persons.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/net/ppp_synctty.c

@@ -29,7 +29,7 @@
  * PPP driver, written by Michael Callahan and Al Longyear, and
  * subsequently hacked by Paul Mackerras.
  *
- * ==FILEVERSION 20020125==
+ * ==FILEVERSION 20040616==
  */
 
 #include <linux/module.h>
@@ -65,7 +65,9 @@ struct syncppp {
 	struct sk_buff	*tpkt;
 	unsigned long	last_xmit;
 
-	struct sk_buff	*rpkt;
+	struct sk_buff_head rqueue;
+
+	struct tasklet_struct tsk;
 
 	atomic_t	refcnt;
 	struct semaphore dead_sem;
@@ -88,6 +90,7 @@ static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
 			  unsigned long arg);
+static void ppp_sync_process(unsigned long arg);
 static int ppp_sync_push(struct syncppp *ap);
 static void ppp_sync_flush_output(struct syncppp *ap);
 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
@@ -217,6 +220,9 @@ ppp_sync_open(struct tty_struct *tty)
 	ap->xaccm[3] = 0x60000000U;
 	ap->raccm = ~0U;
 
+	skb_queue_head_init(&ap->rqueue);
+	tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
+
 	atomic_set(&ap->refcnt, 1);
 	init_MUTEX_LOCKED(&ap->dead_sem);
 
@@ -267,10 +273,10 @@ ppp_sync_close(struct tty_struct *tty)
 	 */
 	if (!atomic_dec_and_test(&ap->refcnt))
 		down(&ap->dead_sem);
+	tasklet_kill(&ap->tsk);
 
 	ppp_unregister_channel(&ap->chan);
-	if (ap->rpkt != 0)
-		kfree_skb(ap->rpkt);
+	skb_queue_purge(&ap->rqueue);
 	if (ap->tpkt != 0)
 		kfree_skb(ap->tpkt);
 	kfree(ap);
@@ -369,17 +375,24 @@ ppp_sync_room(struct tty_struct *tty)
 	return 65535;
 }
 
+/*
+ * This can now be called from hard interrupt level as well
+ * as soft interrupt level or mainline.
+ */
 static void
 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
-		  char *flags, int count)
+		  char *cflags, int count)
 {
 	struct syncppp *ap = sp_get(tty);
+	unsigned long flags;
 
 	if (ap == 0)
 		return;
-	spin_lock_bh(&ap->recv_lock);
-	ppp_sync_input(ap, buf, flags, count);
-	spin_unlock_bh(&ap->recv_lock);
+	spin_lock_irqsave(&ap->recv_lock, flags);
+	ppp_sync_input(ap, buf, cflags, count);
+	spin_unlock_irqrestore(&ap->recv_lock, flags);
+	if (skb_queue_len(&ap->rqueue))
+		tasklet_schedule(&ap->tsk);
 	sp_put(ap);
 	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
 	    && tty->driver->unthrottle)
@@ -394,8 +407,8 @@ ppp_sync_wakeup(struct tty_struct *tty)
 	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 	if (ap == 0)
 		return;
-	if (ppp_sync_push(ap))
-		ppp_output_wakeup(&ap->chan);
+	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
+	tasklet_schedule(&ap->tsk);
 	sp_put(ap);
 }
 
@@ -449,9 +462,9 @@ ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 		if (get_user(val, (int *) arg))
 			break;
 		ap->flags = val & ~SC_RCV_BITS;
-		spin_lock_bh(&ap->recv_lock);
+		spin_lock_irq(&ap->recv_lock);
 		ap->rbits = val & SC_RCV_BITS;
-		spin_unlock_bh(&ap->recv_lock);
+		spin_unlock_irq(&ap->recv_lock);
 		err = 0;
 		break;
 
@@ -511,6 +524,32 @@ ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 	return err;
 }
 
+/*
+ * This is called at softirq level to deliver received packets
+ * to the ppp_generic code, and to tell the ppp_generic code
+ * if we can accept more output now.
+ */
+static void ppp_sync_process(unsigned long arg)
+{
+	struct syncppp *ap = (struct syncppp *) arg;
+	struct sk_buff *skb;
+
+	/* process received packets */
+	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
+		if (skb->len == 0) {
+			/* zero length buffers indicate error */
+			ppp_input_error(&ap->chan, 0);
+			kfree_skb(skb);
+		}
+		else
+			ppp_input(&ap->chan, skb);
+	}
+
+	/* try to push more stuff out */
+	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
+		ppp_output_wakeup(&ap->chan);
+}
+
 /*
  * Procedures for encapsulation and framing.
  */
@@ -600,7 +639,6 @@ ppp_sync_push(struct syncppp *ap)
 	struct tty_struct *tty = ap->tty;
 	int tty_stuffed = 0;
 
-	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 	if (!spin_trylock_bh(&ap->xmit_lock))
 		return 0;
 	for (;;) {
@@ -667,41 +705,6 @@ ppp_sync_flush_output(struct syncppp *ap)
  * Receive-side routines.
  */
 
-static inline void
-process_input_packet(struct syncppp *ap)
-{
-	struct sk_buff *skb;
-	unsigned char *p;
-	int code = 0;
-
-	skb = ap->rpkt;
-	ap->rpkt = 0;
-
-	/* strip address/control field if present */
-	p = skb->data;
-	if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
-		/* chop off address/control */
-		if (skb->len < 3)
-			goto err;
-		p = skb_pull(skb, 2);
-	}
-
-	/* decompress protocol field if compressed */
-	if (p[0] & 1) {
-		/* protocol is compressed */
-		skb_push(skb, 1)[0] = 0;
-	} else if (skb->len < 2)
-		goto err;
-
-	/* pass to generic layer */
-	ppp_input(&ap->chan, skb);
-	return;
-
- err:
-	kfree_skb(skb);
-	ppp_input_error(&ap->chan, code);
-}
-
 /* called when the tty driver has data for us.
  *
  * Data is frame oriented: each call to ppp_sync_input is considered
@@ -713,39 +716,59 @@ ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
 		char *flags, int count)
 {
 	struct sk_buff *skb;
-	unsigned char *sp;
+	unsigned char *p;
 
 	if (count == 0)
 		return;
 
-	/* if flag set, then error, ignore frame */
-	if (flags != 0 && *flags) {
-		ppp_input_error(&ap->chan, *flags);
-		return;
-	}
-
 	if (ap->flags & SC_LOG_INPKT)
 		ppp_print_buffer ("receive buffer", buf, count);
 
 	/* stuff the chars in the skb */
-	if ((skb = ap->rpkt) == 0) {
 	if ((skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2)) == 0) {
 		printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
-			ppp_input_error(&ap->chan, 0);
-			return;
+		goto err;
 	}
 	/* Try to get the payload 4-byte aligned */
 	if (buf[0] != PPP_ALLSTATIONS)
 		skb_reserve(skb, 2 + (buf[0] & 1));
-		ap->rpkt = skb;
-	}
-	if (count > skb_tailroom(skb)) {
+
+	if (flags != 0 && *flags) {
+		/* error flag set, ignore frame */
+		goto err;
+	} else if (count > skb_tailroom(skb)) {
 		/* packet overflowed MRU */
-		ppp_input_error(&ap->chan, 1);
-	} else {
-		sp = skb_put(skb, count);
-		memcpy(sp, buf, count);
-		process_input_packet(ap);
+		goto err;
+	}
+
+	p = skb_put(skb, count);
+	memcpy(p, buf, count);
+
+	/* strip address/control field if present */
+	p = skb->data;
+	if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
+		/* chop off address/control */
+		if (skb->len < 3)
+			goto err;
+		p = skb_pull(skb, 2);
+	}
+
+	/* decompress protocol field if compressed */
+	if (p[0] & 1) {
+		/* protocol is compressed */
+		skb_push(skb, 1)[0] = 0;
+	} else if (skb->len < 2)
+		goto err;
+
+	/* queue the frame to be processed */
+	skb_queue_tail(&ap->rqueue, skb);
+	return;
+
+err:
+	/* queue zero length packet as error indication */
+	if (skb || (skb = dev_alloc_skb(0))) {
+		skb_trim(skb, 0);
+		skb_queue_tail(&ap->rqueue, skb);
 	}
 }