Commit 88df16f8 authored by Eric Dumazet's avatar Eric Dumazet Committed by Paolo Abeni
Browse files

net: sched: calls synchronize_net() only when needed 



dev_deactivate_many() role is to remove the qdiscs
of a network device.

When/if a qdisc is dismantled, an rcu grace period
is needed to make sure all outstanding qdisc enqueue
are done before we proceed with a qdisc reset.

Most virtual devices do not have a qdisc.

We can call the expensive synchronize_net() only
if needed.

Note that dev_deactivate_many() does not have to deal
with qdisc-less dev_queue_xmit, as an old comment
was claiming.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250109171850.2871194-1-edumazet@google.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent a833fb85

net/sched/sch_generic.c

+11 −11
Original line number Diff line number Diff line
@@ -1277,15 +1277,17 @@ static void qdisc_deactivate(struct Qdisc *qdisc) 


static void dev_deactivate_queue(struct net_device *dev,

				 struct netdev_queue *dev_queue,

				 void *_qdisc_default)

				 void *_sync_needed)

{

	struct Qdisc *qdisc_default = _qdisc_default;

	bool *sync_needed = _sync_needed;

	struct Qdisc *qdisc;



	qdisc = rtnl_dereference(dev_queue->qdisc);

	if (qdisc) {

		if (qdisc->enqueue)

			*sync_needed = true;

		qdisc_deactivate(qdisc);

		rcu_assign_pointer(dev_queue->qdisc, qdisc_default);

		rcu_assign_pointer(dev_queue->qdisc, &noop_qdisc);

	}

}
@@ -1352,23 +1354,21 @@ static bool some_qdisc_is_busy(struct net_device *dev) 
 */

void dev_deactivate_many(struct list_head *head)

{

	bool sync_needed = false;

	struct net_device *dev;



	list_for_each_entry(dev, head, close_list) {

		netdev_for_each_tx_queue(dev, dev_deactivate_queue,

					 &noop_qdisc);

					 &sync_needed);

		if (dev_ingress_queue(dev))

			dev_deactivate_queue(dev, dev_ingress_queue(dev),

					     &noop_qdisc);

					     &sync_needed);



		netdev_watchdog_down(dev);

	}



	/* Wait for outstanding qdisc-less dev_queue_xmit calls or

	 * outstanding qdisc enqueuing calls.

	 * This is avoided if all devices are in dismantle phase :

	 * Caller will call synchronize_net() for us

	 */

	/* Wait for outstanding qdisc enqueuing calls. */

	if (sync_needed)

		synchronize_net();



	list_for_each_entry(dev, head, close_list) {