wimax/i2400m: fix i2400m->wake_tx_skb handling

i2400m_net_wake_tx() sets ->wake_tx_skb with the given skb if
->wake_tx_ws is not pending; however, i2400m_wake_tx_work() could have
just started execution and haven't fetched -><wake_tx_skb yet.  The
previous packet will be leaked.

Update ->wake_tx_skb handling.

* i2400m_net_wake_tx() now tests whether the previous ->wake_tx_skb
  has been consumed by ->wake_tx_ws instead of testing work_pending().

* i2400m_net_wake_stop() is simplified similarly.  It always puts
  ->wake_tx_skb if non-NULL.

* Spurious ->wake_tx_skb dereference outside critical section dropped
  from i2400m_wake_tx_work().

Only compile tested.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Dan Williams <dcbw@redhat.com>
Cc: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
Cc: linux-wimax@intel.com
Cc: wimax@linuxwimax.org

drivers/net/wimax/i2400m/netdev.c

@@ -156,7 +156,7 @@ void i2400m_wake_tx_work(struct work_struct *ws)
 	struct i2400m *i2400m = container_of(ws, struct i2400m, wake_tx_ws);
 	struct net_device *net_dev = i2400m->wimax_dev.net_dev;
 	struct device *dev = i2400m_dev(i2400m);
-	struct sk_buff *skb = i2400m->wake_tx_skb;
+	struct sk_buff *skb;
 	unsigned long flags;
 
 	spin_lock_irqsave(&i2400m->tx_lock, flags);
@@ -236,23 +236,26 @@ void i2400m_tx_prep_header(struct sk_buff *skb)
 void i2400m_net_wake_stop(struct i2400m *i2400m)
 {
 	struct device *dev = i2400m_dev(i2400m);
+	struct sk_buff *wake_tx_skb;
+	unsigned long flags;
 
 	d_fnstart(3, dev, "(i2400m %p)\n", i2400m);
-	/* See i2400m_hard_start_xmit(), references are taken there
-	 * and here we release them if the work was still
-	 * pending. Note we can't differentiate work not pending vs
-	 * never scheduled, so the NULL check does that. */
-	if (cancel_work_sync(&i2400m->wake_tx_ws) == 0
-	    && i2400m->wake_tx_skb != NULL) {
-		unsigned long flags;
-		struct sk_buff *wake_tx_skb;
+	/*
+	 * See i2400m_hard_start_xmit(), references are taken there and
+	 * here we release them if the packet was still pending.
+	 */
+	cancel_work_sync(&i2400m->wake_tx_ws);
+
 	spin_lock_irqsave(&i2400m->tx_lock, flags);
-		wake_tx_skb = i2400m->wake_tx_skb;	/* compat help */
-		i2400m->wake_tx_skb = NULL;	/* compat help */
+	wake_tx_skb = i2400m->wake_tx_skb;
+	i2400m->wake_tx_skb = NULL;
 	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+
+	if (wake_tx_skb) {
 		i2400m_put(i2400m);
 		kfree_skb(wake_tx_skb);
 	}
+
 	d_fnend(3, dev, "(i2400m %p) = void\n", i2400m);
 }
 
@@ -288,7 +291,7 @@ int i2400m_net_wake_tx(struct i2400m *i2400m, struct net_device *net_dev,
 	 * and if pending, release those resources. */
 	result = 0;
 	spin_lock_irqsave(&i2400m->tx_lock, flags);
-	if (!work_pending(&i2400m->wake_tx_ws)) {
+	if (!i2400m->wake_tx_skb) {
 		netif_stop_queue(net_dev);
 		i2400m_get(i2400m);
 		i2400m->wake_tx_skb = skb_get(skb);	/* transfer ref count */