netdev - [net-next PATCH 3/3] net: sched: fall back to noqueue when removing root qdisc

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Date:	Fri, 21 Aug 2015 17:58:08 +0200
From:	Phil Sutter <phil@....cc>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, eric.dumazet@...il.com, brouer@...hat.com
Subject: [net-next PATCH 3/3] net: sched: fall back to noqueue when removing root qdisc

When removing the root qdisc, the interface should fall back to noqueue
as the 'real' minimal qdisc instead of the default one. Therefore
dev_graft_qdisc() has to be adjusted to assign noqueue if NULL was
passed as new qdisc, and qdisc_graft() needs to assign noqueue to
dev->qdisc instead of noop to prevent dev_activate() from attaching
default qdiscs to the interface.

Note that it is also necessary to have dev_graft_qdisc() set
dev_queue->qdisc to the new qdisc instead of (unconditionally) noop. I
don't know why this was there at all (originates from pre-git time), but
it seems wrong to me.  It could be worked around by droping the extra
check for noqueue in transition_one_qdisc(), maybe with unintended
side-effects.

Signed-off-by: Phil Sutter <phil@....cc>
---
 net/sched/sch_api.c     | 2 +-
 net/sched/sch_generic.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 224374c..3b2cf30 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -839,7 +839,7 @@ skip:
 					   dev->qdisc, new);
 			if (new && !new->ops->attach)
 				atomic_inc(&new->refcnt);
-			dev->qdisc = new ? : &noop_qdisc;
+			dev->qdisc = new ? : &noqueue_qdisc;

 			if (new && new->ops->attach)
 				new->ops->attach(new);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index ab614ee..556de30 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -723,9 +723,9 @@ struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue,

 	/* ... and graft new one */
 	if (qdisc == NULL)
-		qdisc = &noop_qdisc;
+		qdisc = &noqueue_qdisc;
 	dev_queue->qdisc_sleeping = qdisc;
-	rcu_assign_pointer(dev_queue->qdisc, &noop_qdisc);
+	rcu_assign_pointer(dev_queue->qdisc, qdisc);

 	spin_unlock_bh(root_lock);

-- 
2.1.2

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