[PATCH net] xen-netback: clear vif->task on disconnect

[Paul Durrant <paul.durrant@citrix.com>]

xenvif_start_xmit() relies on checking vif->task for NULL to determine
whether the vif is ready to accept packets. The task thread is stopped in
xenvif_disconnect() but task is not set to NULL. Thus, on a re-connect the
check will give a false positive.
Also since commit ea732dff5cfa10789007bf4a5b935388a0bb2a8f it should not
be possible for xenvif_connect() to be called if the vif is already connected
so change the check of vif->tx_irq to a BUG_ON() and also add a
BUG_ON(vif->task).

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
---
 drivers/net/xen-netback/interface.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 2329ccc..d42efbf 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -370,9 +370,8 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
 {
 	int err = -ENOMEM;
 
-	/* Already connected through? */
-	if (vif->tx_irq)
-		return 0;
+	BUG_ON(vif->tx_irq);
+	BUG_ON(vif->task);
 
 	err = xenvif_map_frontend_rings(vif, tx_ring_ref, rx_ring_ref);
 	if (err < 0)
@@ -461,8 +460,10 @@ void xenvif_disconnect(struct xenvif *vif)
 	if (netif_carrier_ok(vif->dev))
 		xenvif_carrier_off(vif);
 
-	if (vif->task)
+	if (vif->task) {
 		kthread_stop(vif->task);
+		vif->task = NULL;
+	}
 
 	if (vif->tx_irq) {
 		if (vif->tx_irq == vif->rx_irq)
-- 
1.7.10.4