netdev - [Patch net-next 5/5] net_sched: get rid of unnecessary dev_qdisc

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Date:   Tue, 26 May 2020 21:35:27 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     vaclav.zindulka@...pnet.cz, Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: [Patch net-next 5/5] net_sched: get rid of unnecessary dev_qdisc_reset()

Resetting old qdisc on dev_queue->qdisc_sleeping in
dev_qdisc_reset() is redundant, because this qdisc,
even if not same with dev_queue->qdisc, is reset via
qdisc_put() right after calling dev_graft_qdisc() when
hitting refcnt 0.

This is very easy to observe with qdisc_reset() tracepoint
and stack traces.

Reported-by: Václav Zindulka <vaclav.zindulka@...pnet.cz>
Tested-by: Václav Zindulka <vaclav.zindulka@...pnet.cz>
Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/sched/sch_generic.c | 16 ----------------
 1 file changed, 16 deletions(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index d13e27467470..b19a0021a0bd 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1191,16 +1191,6 @@ 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
@@ -1237,12 +1227,6 @@ void dev_deactivate_many(struct list_head *head)
 			 */
 			schedule_timeout_uninterruptible(1);
 		}
-		/* 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);
 	}
 }
 
-- 
2.26.2