linux-kernel - [PATCH 4.15 109/128] net: sched: drop qdisc_reset from dev_graft

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Message-Id: <20180316152341.971330169@linuxfoundation.org>
Date:   Fri, 16 Mar 2018 16:24:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, John Fastabend <john.fastabend@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.15 109/128] net: sched: drop qdisc_reset from dev_graft_qdisc

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: John Fastabend <john.fastabend@...il.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@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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)