[PATCH 4.15 109/128] net: sched: drop qdisc_reset from dev_graft_qdisc

Greg Kroah-Hartman
2018-03-16T15:44:17Z

From: John Fastabend <john.fastabend@gmail.com>

[ Upstream commit 7bbde83b1860c28a1cc35516352c4e7e5172c29a ]

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: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/sch_generic.c | 28 +++++++++++++++++++---------
1 file changed, 19 insertions(+), 9 deletions(-)

--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -762,10 +762,6 @@ struct Qdisc *dev_graft_qdisc(struct net
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;
@@ -916,6 +912,16 @@ static bool some_qdisc_is_busy(struct ne
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
@@ -926,7 +932,6 @@ static bool some_qdisc_is_busy(struct ne
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,
@@ -936,20 +941,25 @@ void dev_deactivate_many(struct list_hea
&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();
+ 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)