[NETPOLL] netconsole: fix soft lockup when removing module

#1
Until kernel ver. 2.6.21 (including) cancel_rearming_delayed_work()
required a work function should always (unconditionally) rearm with
delay > 0 - otherwise it would endlessly loop. This patch replaces
this function with cancel_delayed_work(). Later kernel versions don't
require this, so here it's only for uniformity.

#2
After deleting a timer in cancel_[rearming_]delayed_work() there could
stay a last skb queued in npinfo->txq causing a memory leak after
kfree(npinfo).

Initial patch & testing by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/netpoll.c

@@ -72,6 +72,7 @@ static void queue_process(struct work_struct *work)
 			netif_tx_unlock(dev);
 			local_irq_restore(flags);
 
+			if (atomic_read(&npinfo->refcnt))
 				schedule_delayed_work(&npinfo->tx_work, HZ/10);
 			return;
 		}
@@ -785,9 +786,15 @@ void netpoll_cleanup(struct netpoll *np)
 			if (atomic_dec_and_test(&npinfo->refcnt)) {
 				skb_queue_purge(&npinfo->arp_tx);
 				skb_queue_purge(&npinfo->txq);
-				cancel_rearming_delayed_work(&npinfo->tx_work);
+				cancel_delayed_work(&npinfo->tx_work);
 				flush_scheduled_work();
 
+				/* clean after last, unfinished work */
+				if (!skb_queue_empty(&npinfo->txq)) {
+					struct sk_buff *skb;
+					skb = __skb_dequeue(&npinfo->txq);
+					kfree_skb(skb);
+				}
 				kfree(npinfo);
 			}
 		}