Commit b37c0fbe authored by Alexander Duyck's avatar Alexander Duyck Committed by Jeff Kirsher
Browse files

net: Add memory barriers to prevent possible race in byte queue limits 



This change adds a memory barrier to the byte queue limit code to address a
possible race as has been seen in the past with the
netif_stop_queue/netif_wake_queue logic.

Signed-off-by: default avatarAlexander Duyck <alexander.h.duyck@intel.com>
Tested-by: default avatarStephen Ko <stephen.s.ko@intel.com>
Signed-off-by: default avatarJeff Kirsher <jeffrey.t.kirsher@intel.com>
parent 5c490354

include/linux/netdevice.h

+33 −16
Original line number Diff line number Diff line
@@ -1899,12 +1899,22 @@ static inline void netdev_tx_sent_queue(struct netdev_queue *dev_queue, 
{

#ifdef CONFIG_BQL

	dql_queued(&dev_queue->dql, bytes);

	if (unlikely(dql_avail(&dev_queue->dql) < 0)) {



	if (likely(dql_avail(&dev_queue->dql) >= 0))

		return;



	set_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state);



	/*

	 * The XOFF flag must be set before checking the dql_avail below,

	 * because in netdev_tx_completed_queue we update the dql_completed

	 * before checking the XOFF flag.

	 */

	smp_mb();



	/* check again in case another CPU has just made room avail */

	if (unlikely(dql_avail(&dev_queue->dql) >= 0))

			clear_bit(__QUEUE_STATE_STACK_XOFF,

			    &dev_queue->state);

	}

		clear_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state);

#endif

}
@@ -1917,16 +1927,23 @@ static inline void netdev_tx_completed_queue(struct netdev_queue *dev_queue, 
					     unsigned pkts, unsigned bytes)

{

#ifdef CONFIG_BQL

	if (likely(bytes)) {

	if (unlikely(!bytes))

		return;



	dql_completed(&dev_queue->dql, bytes);

		if (unlikely(test_bit(__QUEUE_STATE_STACK_XOFF,

		    &dev_queue->state) &&

		    dql_avail(&dev_queue->dql) >= 0)) {

			if (test_and_clear_bit(__QUEUE_STATE_STACK_XOFF,

			     &dev_queue->state))



	/*

	 * Without the memory barrier there is a small possiblity that

	 * netdev_tx_sent_queue will miss the update and cause the queue to

	 * be stopped forever

	 */

	smp_mb();



	if (dql_avail(&dev_queue->dql) < 0)

		return;



	if (test_and_clear_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state))

		netif_schedule_queue(dev_queue);

		}

	}

#endif

}