netback: fix shutting down the ring if it contains garbage

Using rtnl_lock() in tasklet context is not permitted.

This undoes the part of 1219:5108c6901b30 that split off
xenvif_carrier_off() from netif_disconnect().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/netback/common.h
+++ b/drivers/xen/netback/common.h
@@ -78,6 +78,8 @@ typedef struct netif_st {
 	u8 can_queue:1;	/* can queue packets for receiver? */
 	u8 copying_receiver:1;	/* copy packets to receiver?       */
 
+	u8 busted:1;
+
 	/* Allow netif_be_start_xmit() to peek ahead in the rx request ring. */
 	RING_IDX rx_req_cons_peek;
 
@@ -195,7 +197,8 @@ int netif_map(netif_t *netif, unsigned l
 void netif_xenbus_init(void);
 
 #define netif_schedulable(netif)				\
-	(netif_running((netif)->dev) && netback_carrier_ok(netif))
+	(likely(!(netif)->busted) &&				\
+	 netif_running((netif)->dev) &&	netback_carrier_ok(netif))
 
 void netif_schedule_work(netif_t *netif);
 void netif_deschedule_work(netif_t *netif);
@@ -204,9 +207,6 @@ int netif_be_start_xmit(struct sk_buff *
 struct net_device_stats *netif_be_get_stats(struct net_device *dev);
 irqreturn_t netif_be_int(int irq, void *dev_id, struct pt_regs *regs);
 
-/* Prevent the device from generating any further traffic. */
-void xenvif_carrier_off(netif_t *netif);
-
 static inline int netbk_can_queue(struct net_device *dev)
 {
 	netif_t *netif = netdev_priv(dev);
--- a/drivers/xen/netback/interface.c
+++ b/drivers/xen/netback/interface.c
@@ -56,6 +56,7 @@ module_param_named(queue_length, netbk_q
 
 static void __netif_up(netif_t *netif)
 {
+	netif->busted = 0;
 	enable_irq(netif->irq);
 	netif_schedule_work(netif);
 }
@@ -347,23 +348,19 @@ err_rx:
 	return err;
 }
 
-void xenvif_carrier_off(netif_t *netif)
-{
-	rtnl_lock();
-	netback_carrier_off(netif);
-	netif_carrier_off(netif->dev); /* discard queued packets */
-	if (netif_running(netif->dev))
-		__netif_down(netif);
-	rtnl_unlock();
-	netif_put(netif);
-}
-
 void netif_disconnect(struct backend_info *be)
 {
 	netif_t *netif = be->netif;
 
-	if (netback_carrier_ok(netif))
-		xenvif_carrier_off(netif);
+	if (netback_carrier_ok(netif)) {
+		rtnl_lock();
+		netback_carrier_off(netif);
+		netif_carrier_off(netif->dev); /* discard queued packets */
+		if (netif_running(netif->dev))
+			__netif_down(netif);
+		rtnl_unlock();
+		netif_put(netif);
+	}
 
 	atomic_dec(&netif->refcnt);
 	wait_event(netif->waiting_to_free, atomic_read(&netif->refcnt) == 0);
--- a/drivers/xen/netback/netback.c
+++ b/drivers/xen/netback/netback.c
@@ -845,7 +845,7 @@ void netif_schedule_work(netif_t *netif)
 	RING_FINAL_CHECK_FOR_REQUESTS(&netif->tx, more_to_do);
 #endif
 
-	if (more_to_do) {
+	if (more_to_do && likely(!netif->busted)) {
 		add_to_net_schedule_list_tail(netif);
 		maybe_schedule_tx_action();
 	}
@@ -1024,7 +1024,9 @@ static void netbk_fatal_tx_err(netif_t *
 {
 	printk(KERN_ERR "%s: fatal error; disabling device\n",
 	       netif->dev->name);
-	xenvif_carrier_off(netif);
+	netif->busted = 1;
+	disable_irq(netif->irq);
+	netif_deschedule_work(netif);
 	netif_put(netif);
 }
 
@@ -1292,6 +1294,11 @@ static void net_tx_action(unsigned long 
 		if (!netif)
 			continue;
 
+		if (unlikely(netif->busted)) {
+			netif_put(netif);
+			continue;
+		}
+
 		if (netif->tx.sring->req_prod - netif->tx.req_cons >
 		    NET_TX_RING_SIZE) {
 			printk(KERN_ERR "%s: Impossible number of requests. "