This is a note to let you know that I've just added the patch titled

net: sched: drop qdisc_reset from dev_graft_qdisc

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: net-sched-drop-qdisc_reset-from-dev_graft_qdisc.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Fri Mar 16 15:11:08 CET 2018

From: John Fastabend john.fastabend@gmail.com Date: Thu, 7 Dec 2017 09:56:04 -0800 Subject: net: sched: drop qdisc_reset from dev_graft_qdisc

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)

Patches currently in stable-queue which might be from john.fastabend@gmail.com are

queue-4.15/net-sched-drop-qdisc_reset-from-dev_graft_qdisc.patch queue-4.15/bpf-fix-stack-state-printing-in-verifier-log.patch