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net: sched: calls synchronize_net() only when needed

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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: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250109171850.2871194-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2025-01-09 17:18:50 +00:00 committed by Paolo Abeni
parent a833fb852e
commit 88df16f851
1 changed files with 11 additions and 11 deletions
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22
net/sched/sch_generic.c
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@ -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);
}
}
@ -1352,24 +1354,22 @@ 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
*/
synchronize_net();
/* Wait for outstanding qdisc enqueuing calls. */
if (sync_needed)
synchronize_net();
list_for_each_entry(dev, head, close_list) {
netdev_for_each_tx_queue(dev, dev_reset_queue, NULL);