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Commit 7bbde83b authored by John Fastabend's avatar John Fastabend Committed by David S. Miller
Browse files

net: sched: drop qdisc_reset from dev_graft_qdisc 



In qdisc_graft_qdisc a "new" qdisc is attached and the 'qdisc_destroy'
operation is called on the old qdisc. The destroy operation will wait
a rcu grace period and call qdisc_rcu_free(). At which point
gso_cpu_skb is free'd along with all stats so no need to zero stats
and gso_cpu_skb from the graft operation itself.

Further after dropping the qdisc locks we can not continue to call
qdisc_reset before waiting an rcu grace period so that the qdisc is
detached from all cpus. By removing the qdisc_reset() here we get
the correct property of waiting an rcu grace period and letting the
qdisc_destroy operation clean up the qdisc correctly.

Note, a refcnt greater than 1 would cause the destroy operation to
be aborted however if this ever happened the reference to the qdisc
would be lost and we would have a memory leak.

Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a53851e2

net/sched/sch_generic.c

+19 −9
Original line number Diff line number Diff line
@@ -819,10 +819,6 @@ struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue, 
	root_lock = qdisc_lock(oqdisc);

	spin_lock_bh(root_lock);



	/* Prune old scheduler */

	if (oqdisc && refcount_read(&oqdisc->refcnt) <= 1)

		qdisc_reset(oqdisc);



	/* ... and graft new one */

	if (qdisc == NULL)

		qdisc = &noop_qdisc;
@@ -977,6 +973,16 @@ static bool some_qdisc_is_busy(struct net_device *dev) 
	return false;

}



static void dev_qdisc_reset(struct net_device *dev,

			    struct netdev_queue *dev_queue,

			    void *none)

{

	struct Qdisc *qdisc = dev_queue->qdisc_sleeping;



	if (qdisc)

		qdisc_reset(qdisc);

}



/**

 * 	dev_deactivate_many - deactivate transmissions on several devices

 * 	@head: list of devices to deactivate
@@ -987,7 +993,6 @@ static bool some_qdisc_is_busy(struct net_device *dev) 
void dev_deactivate_many(struct list_head *head)

{

	struct net_device *dev;

	bool sync_needed = false;



	list_for_each_entry(dev, head, close_list) {

		netdev_for_each_tx_queue(dev, dev_deactivate_queue,
@@ -997,20 +1002,25 @@ void dev_deactivate_many(struct list_head *head) 
					     &noop_qdisc);



		dev_watchdog_down(dev);

		sync_needed |= !dev->dismantle;

	}



	/* Wait for outstanding qdisc-less dev_queue_xmit calls.

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

	 * Caller will call synchronize_net() for us

	 */

	if (sync_needed)

	synchronize_net();



	/* Wait for outstanding qdisc_run calls. */

	list_for_each_entry(dev, head, close_list)

	list_for_each_entry(dev, head, close_list) {

		while (some_qdisc_is_busy(dev))

			yield();

		/* The new qdisc is assigned at this point so we can safely

		 * unwind stale skb lists and qdisc statistics

		 */

		netdev_for_each_tx_queue(dev, dev_qdisc_reset, NULL);

		if (dev_ingress_queue(dev))

			dev_qdisc_reset(dev, dev_ingress_queue(dev), NULL);

	}

}



void dev_deactivate(struct net_device *dev)