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Date: Thu, 07 Dec 2017 09:56:04 -0800 From: John Fastabend <john.fastabend@...il.com> To: willemdebruijn.kernel@...il.com, daniel@...earbox.net, eric.dumazet@...il.com, davem@...emloft.net Cc: netdev@...r.kernel.org, jiri@...nulli.us, xiyou.wangcong@...il.com Subject: [net-next PATCH 07/14] 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: John Fastabend <john.fastabend@...il.com> --- net/sched/sch_generic.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index dfeabe3..482ba22 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -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(); + 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)
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