[PATCHv2 net] usbnet: fix cyclical race on disconnect with work queue

[Oliver Neukum]

The work can submit URBs and the URBs can schedule the work.
This cycle needs to be broken, when a device is to be stopped.
Use a flag to do so.
This is a design issue as old as the driver.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
CC: stable@xxxxxxxxxxxxxxx
---

v2: fix PM reference issue

 drivers/net/usb/usbnet.c   | 37 ++++++++++++++++++++++++++++---------
 include/linux/usb/usbnet.h | 17 +++++++++++++++++
 2 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 18eb5ba436df..2506aa8c603e 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -464,10 +464,15 @@ static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb,
 void usbnet_defer_kevent (struct usbnet *dev, int work)
 {
 	set_bit (work, &dev->flags);
-	if (!schedule_work (&dev->kevent))
-		netdev_dbg(dev->net, "kevent %s may have been dropped\n", usbnet_event_names[work]);
-	else
-		netdev_dbg(dev->net, "kevent %s scheduled\n", usbnet_event_names[work]);
+	if (!usbnet_going_away(dev)) {
+		if (!schedule_work(&dev->kevent))
+			netdev_dbg(dev->net,
+				   "kevent %s may have been dropped\n",
+				   usbnet_event_names[work]);
+		else
+			netdev_dbg(dev->net,
+				   "kevent %s scheduled\n", usbnet_event_names[work]);
+	}
 }
 EXPORT_SYMBOL_GPL(usbnet_defer_kevent);
 
@@ -535,7 +540,8 @@ static int rx_submit (struct usbnet *dev, struct urb *urb, gfp_t flags)
 			tasklet_schedule (&dev->bh);
 			break;
 		case 0:
-			__usbnet_queue_skb(&dev->rxq, skb, rx_start);
+			if (!usbnet_going_away(dev))
+				__usbnet_queue_skb(&dev->rxq, skb, rx_start);
 		}
 	} else {
 		netif_dbg(dev, ifdown, dev->net, "rx: stopped\n");
@@ -843,9 +849,18 @@ int usbnet_stop (struct net_device *net)
 
 	/* deferred work (timer, softirq, task) must also stop */
 	dev->flags = 0;
-	del_timer_sync (&dev->delay);
-	tasklet_kill (&dev->bh);
+	del_timer_sync(&dev->delay);
+	tasklet_kill(&dev->bh);
 	cancel_work_sync(&dev->kevent);
+
+	/* We have cyclic dependencies. Those calls are needed
+	 * to break a cycle. We cannot fall into the gaps because
+	 * we have a flag
+	 */
+	tasklet_kill(&dev->bh);
+	del_timer_sync(&dev->delay);
+	cancel_work_sync(&dev->kevent);
+
 	if (!pm)
 		usb_autopm_put_interface(dev->intf);
 
@@ -1171,7 +1186,8 @@ usbnet_deferred_kevent (struct work_struct *work)
 					   status);
 		} else {
 			clear_bit (EVENT_RX_HALT, &dev->flags);
-			tasklet_schedule (&dev->bh);
+			if (!usbnet_going_away(dev))
+				tasklet_schedule(&dev->bh);
 		}
 	}
 
@@ -1196,7 +1212,8 @@ usbnet_deferred_kevent (struct work_struct *work)
 			usb_autopm_put_interface(dev->intf);
 fail_lowmem:
 			if (resched)
-				tasklet_schedule (&dev->bh);
+				if (!usbnet_going_away(dev))
+					tasklet_schedule(&dev->bh);
 		}
 	}
 
@@ -1559,6 +1576,7 @@ static void usbnet_bh (struct timer_list *t)
 	} else if (netif_running (dev->net) &&
 		   netif_device_present (dev->net) &&
 		   netif_carrier_ok(dev->net) &&
+		   !usbnet_going_away(dev) &&
 		   !timer_pending(&dev->delay) &&
 		   !test_bit(EVENT_RX_PAUSED, &dev->flags) &&
 		   !test_bit(EVENT_RX_HALT, &dev->flags)) {
@@ -1606,6 +1624,7 @@ void usbnet_disconnect (struct usb_interface *intf)
 	usb_set_intfdata(intf, NULL);
 	if (!dev)
 		return;
+	usbnet_mark_going_away(dev);
 
 	xdev = interface_to_usbdev (intf);
 
diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h
index 9f08a584d707..d02d6f16da46 100644
--- a/include/linux/usb/usbnet.h
+++ b/include/linux/usb/usbnet.h
@@ -76,8 +76,25 @@ struct usbnet {
 #		define EVENT_LINK_CHANGE	11
 #		define EVENT_SET_RX_MODE	12
 #		define EVENT_NO_IP_ALIGN	13
+/* This one is special, as it indicates that the device is going away
+ * there are cyclic dependencies between tasklet, timer and bh
+ * that must be broken
+ */
+#		define EVENT_UNPLUG		31
 };
 
+static inline bool usbnet_going_away(struct usbnet *ubn)
+{
+	smp_mb__before_atomic(); /* against usbnet_mark_going_away() */
+	return test_bit(EVENT_UNPLUG, &ubn->flags);
+}
+
+static inline void usbnet_mark_going_away(struct usbnet *ubn)
+{
+	set_bit(EVENT_UNPLUG, &ubn->flags);
+	smp_mb__after_atomic(); /* against usbnet_going_away() */
+}
+
 static inline struct usb_driver *driver_of(struct usb_interface *intf)
 {
 	return to_usb_driver(intf->dev.driver);
-- 
2.45.2