i4l: Fix random hard freeze with AVM c4 card

The patch
- Includes the call to capilib_data_b3_req in the spinlock. This routine
  in turn calls the offending mq_enqueue routine that triggered the
  freeze if not locked.  This should also fix other indicators of
  incosistent capilib_msgidqueue list, that trigger messages like:
  Oct  5 03:05:57 BERL0 kernel: kcapi: msgid 3019 ncci 0x30301 not on queue
  that we saw several times a day (usually several in a row).
- Fixes all occurrences of c4_dispatch_tx to be called with active
  spinlock, there were some instances where no lock was active. Mostly
  these are in very infrequently called routines, so the additional
  performance penalty is minimal.

Signed-off-by: Karsten Keil <kkeil@suse.de>
Signed-off-by: Rainer Brestan <rainer.brestan@frequentis.com>
Signed-off-by: Ralf Schlatterbeck <rsc@runtux.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/isdn/hardware/avm/c4.c

@@ -727,6 +727,7 @@ static void c4_send_init(avmcard *card)
 {
 	struct sk_buff *skb;
 	void *p;
+	unsigned long flags;
 
 	skb = alloc_skb(15, GFP_ATOMIC);
 	if (!skb) {
@@ -744,12 +745,15 @@ static void c4_send_init(avmcard *card)
 	skb_put(skb, (u8 *)p - (u8 *)skb->data);
 
 	skb_queue_tail(&card->dma->send_queue, skb);
+	spin_lock_irqsave(&card->lock, flags);
 	c4_dispatch_tx(card);
+	spin_unlock_irqrestore(&card->lock, flags);
 }
 
 static int queue_sendconfigword(avmcard *card, u32 val)
 {
 	struct sk_buff *skb;
+	unsigned long flags;
 	void *p;
 
 	skb = alloc_skb(3+4, GFP_ATOMIC);
@@ -766,7 +770,9 @@ static int queue_sendconfigword(avmcard *card, u32 val)
 	skb_put(skb, (u8 *)p - (u8 *)skb->data);
 
 	skb_queue_tail(&card->dma->send_queue, skb);
+	spin_lock_irqsave(&card->lock, flags);
 	c4_dispatch_tx(card);
+	spin_unlock_irqrestore(&card->lock, flags);
 	return 0;
 }
 
@@ -986,7 +992,9 @@ static void c4_release_appl(struct capi_ctr *ctrl, u16 appl)
 	struct sk_buff *skb;
 	void *p;
 
+	spin_lock_irqsave(&card->lock, flags);
 	capilib_release_appl(&cinfo->ncci_head, appl);
+	spin_unlock_irqrestore(&card->lock, flags);
 
 	if (ctrl->cnr == card->cardnr) {
 		skb = alloc_skb(7, GFP_ATOMIC);
@@ -1019,7 +1027,8 @@ static u16 c4_send_message(struct capi_ctr *ctrl, struct sk_buff *skb)
 	u16 retval = CAPI_NOERROR;
 	unsigned long flags;
 
- 	if (CAPIMSG_CMD(skb->data) == CAPI_DATA_B3_REQ) {
+	spin_lock_irqsave(&card->lock, flags);
+	if (CAPIMSG_CMD(skb->data) == CAPI_DATA_B3_REQ) {
 		retval = capilib_data_b3_req(&cinfo->ncci_head,
 					     CAPIMSG_APPID(skb->data),
 					     CAPIMSG_NCCI(skb->data),
@@ -1027,10 +1036,9 @@ static u16 c4_send_message(struct capi_ctr *ctrl, struct sk_buff *skb)
 	}
 	if (retval == CAPI_NOERROR) {
 		skb_queue_tail(&card->dma->send_queue, skb);
-		spin_lock_irqsave(&card->lock, flags);
 		c4_dispatch_tx(card);
-		spin_unlock_irqrestore(&card->lock, flags);
 	}
+	spin_unlock_irqrestore(&card->lock, flags);
 	return retval;
 }