net: use an atomic_long_t for queue->trans_timeout

tx_timeout_show() assumed dev_watchdog() would stop all
the queues, to fetch queue->trans_timeout under protection
of the queue->_xmit_lock.

As we want to no longer disrupt transmits, we use an
atomic_long_t instead.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: david decotigny <david.decotigny@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -592,7 +592,7 @@ struct netdev_queue {
 	 * Number of TX timeouts for this queue
 	 * (/sys/class/net/DEV/Q/trans_timeout)
 	 */
-	unsigned long		trans_timeout;
+	atomic_long_t		trans_timeout;
 
 	/* Subordinate device that the queue has been assigned to */
 	struct net_device	*sb_dev;

net/core/net-sysfs.c

@@ -1201,11 +1201,7 @@ static const struct sysfs_ops netdev_queue_sysfs_ops = {
 
 static ssize_t tx_timeout_show(struct netdev_queue *queue, char *buf)
 {
-	unsigned long trans_timeout;
-
-	spin_lock_irq(&queue->_xmit_lock);
-	trans_timeout = queue->trans_timeout;
-	spin_unlock_irq(&queue->_xmit_lock);
+	unsigned long trans_timeout = atomic_long_read(&queue->trans_timeout);
 
 	return sprintf(buf, fmt_ulong, trans_timeout);
 }

net/sched/sch_generic.c

@@ -467,7 +467,7 @@ static void dev_watchdog(struct timer_list *t)
 				    time_after(jiffies, (trans_start +
 							 dev->watchdog_timeo))) {
 					some_queue_timedout = 1;
-					txq->trans_timeout++;
+					atomic_long_inc(&txq->trans_timeout);
 					break;
 				}
 			}