i4l: fix random freezes with AVM B1 drivers

This fix the same issue which was debbuged for the C4 controller for the B1
versions.

The capilib_ function modify or traverse a linked list without locking.

This patch extends the existing locking to the calls of these function to
prevent access to a list which is in the middle of a modification.
Signed-off-by: NKarsten Keil <kkeil@suse.de>
C: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/isdn/hardware/avm/b1.c

@@ -321,12 +321,15 @@ void b1_reset_ctr(struct capi_ctr *ctrl)
 	avmctrl_info *cinfo = (avmctrl_info *)(ctrl->driverdata);
 	avmcard *card = cinfo->card;
 	unsigned int port = card->port;
+	unsigned long flags;
 
 	b1_reset(port);
 	b1_reset(port);
 
 	memset(cinfo->version, 0, sizeof(cinfo->version));
+	spin_lock_irqsave(&card->lock, flags);
 	capilib_release(&cinfo->ncci_head);
+	spin_unlock_irqrestore(&card->lock, flags);
 	capi_ctr_reseted(ctrl);
 }
 
@@ -361,9 +364,8 @@ void b1_release_appl(struct capi_ctr *ctrl, u16 appl)
 	unsigned int port = card->port;
 	unsigned long flags;
 
-	capilib_release_appl(&cinfo->ncci_head, appl);
-
 	spin_lock_irqsave(&card->lock, flags);
+	capilib_release_appl(&cinfo->ncci_head, appl);
 	b1_put_byte(port, SEND_RELEASE);
 	b1_put_word(port, appl);
 	spin_unlock_irqrestore(&card->lock, flags);
@@ -380,27 +382,27 @@ u16 b1_send_message(struct capi_ctr *ctrl, struct sk_buff *skb)
 	u8 subcmd = CAPIMSG_SUBCOMMAND(skb->data);
 	u16 dlen, retval;
 
+	spin_lock_irqsave(&card->lock, flags);
 	if (CAPICMD(cmd, subcmd) == CAPI_DATA_B3_REQ) {
 		retval = capilib_data_b3_req(&cinfo->ncci_head,
 					     CAPIMSG_APPID(skb->data),
 					     CAPIMSG_NCCI(skb->data),
 					     CAPIMSG_MSGID(skb->data));
-		if (retval != CAPI_NOERROR) 
+		if (retval != CAPI_NOERROR) {
+			spin_unlock_irqrestore(&card->lock, flags);
 			return retval;
+		}
 
 		dlen = CAPIMSG_DATALEN(skb->data);
 
-	 	spin_lock_irqsave(&card->lock, flags);
 		b1_put_byte(port, SEND_DATA_B3_REQ);
 		b1_put_slice(port, skb->data, len);
 		b1_put_slice(port, skb->data + len, dlen);
-		spin_unlock_irqrestore(&card->lock, flags);
 	} else {
-	 	spin_lock_irqsave(&card->lock, flags);
 		b1_put_byte(port, SEND_MESSAGE);
 		b1_put_slice(port, skb->data, len);
-		spin_unlock_irqrestore(&card->lock, flags);
 	}
+	spin_unlock_irqrestore(&card->lock, flags);
 
 	dev_kfree_skb_any(skb);
 	return CAPI_NOERROR;
@@ -534,17 +536,17 @@ irqreturn_t b1_interrupt(int interrupt, void *devptr)
 
 		ApplId = (unsigned) b1_get_word(card->port);
 		MsgLen = b1_get_slice(card->port, card->msgbuf);
-		spin_unlock_irqrestore(&card->lock, flags);
 		if (!(skb = alloc_skb(MsgLen, GFP_ATOMIC))) {
 			printk(KERN_ERR "%s: incoming packet dropped\n",
 					card->name);
+			spin_unlock_irqrestore(&card->lock, flags);
 		} else {
 			memcpy(skb_put(skb, MsgLen), card->msgbuf, MsgLen);
 			if (CAPIMSG_CMD(skb->data) == CAPI_DATA_B3_CONF)
 				capilib_data_b3_conf(&cinfo->ncci_head, ApplId,
 						     CAPIMSG_NCCI(skb->data),
 						     CAPIMSG_MSGID(skb->data));
-
+			spin_unlock_irqrestore(&card->lock, flags);
 			capi_ctr_handle_message(ctrl, ApplId, skb);
 		}
 		break;
@@ -554,21 +556,17 @@ irqreturn_t b1_interrupt(int interrupt, void *devptr)
 		ApplId = b1_get_word(card->port);
 		NCCI = b1_get_word(card->port);
 		WindowSize = b1_get_word(card->port);
-		spin_unlock_irqrestore(&card->lock, flags);
-
 		capilib_new_ncci(&cinfo->ncci_head, ApplId, NCCI, WindowSize);
-
+		spin_unlock_irqrestore(&card->lock, flags);
 		break;
 
 	case RECEIVE_FREE_NCCI:
 
 		ApplId = b1_get_word(card->port);
 		NCCI = b1_get_word(card->port);
-		spin_unlock_irqrestore(&card->lock, flags);
-
 		if (NCCI != 0xffffffff)
 			capilib_free_ncci(&cinfo->ncci_head, ApplId, NCCI);
-	       
+		spin_unlock_irqrestore(&card->lock, flags);
 		break;
 
 	case RECEIVE_START: