netdev - Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl

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Message-Id: <20080813.022549.203848195.davem@davemloft.net>
Date:	Wed, 13 Aug 2008 02:25:49 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jarkao2@...il.com
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org
Subject: Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl_lock().

From: Jarek Poplawski <jarkao2@...il.com>
Date: Wed, 13 Aug 2008 06:53:03 +0000

> Otherwise, I think you would better send some code example with these
> flags, so we could be sure there is no misunderstanding around this.

Here it my concrete proposal for a fix.

pkt_sched: Fix queue quiescence testing in dev_deactivate().

Based upon discussions with Jarek P. and Herbert Xu.

First, we're testing the wrong qdisc.  We just reset the device
queue qdiscs to &noop_qdisc and checking it's state is completely
pointless here.

We want to wait until the previous qdisc that was sitting at
the ->qdisc pointer is not busy any more.  And that would be
->qdisc_sleeping.

Because of how we propagate the samples qdisc pointer down into
qdisc_run and friends via per-cpu ->output_queue and netif_schedule,
we have to wait also for the __QDISC_STATE_SCHED bit to clear as
well.

Signed-off-by: David S. Miller <davem@...emloft.net>

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 7cf83b3..4685746 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -647,7 +647,7 @@ static void dev_deactivate_queue(struct net_device *dev,
 	}
 }

-static bool some_qdisc_is_running(struct net_device *dev, int lock)
+static bool some_qdisc_is_busy(struct net_device *dev, int lock)
 {
 	unsigned int i;

@@ -658,13 +658,14 @@ static bool some_qdisc_is_running(struct net_device *dev, int lock)
 		int val;

 		dev_queue = netdev_get_tx_queue(dev, i);
-		q = dev_queue->qdisc;
+		q = dev_queue->qdisc_sleeping;
 		root_lock = qdisc_lock(q);

 		if (lock)
 			spin_lock_bh(root_lock);

-		val = test_bit(__QDISC_STATE_RUNNING, &q->state);
+		val = (test_bit(__QDISC_STATE_RUNNING, &q->state) ||
+		       test_bit(__QDISC_STATE_SCHED, &q->state));

 		if (lock)
 			spin_unlock_bh(root_lock);
@@ -689,14 +690,14 @@ void dev_deactivate(struct net_device *dev)

 	/* Wait for outstanding qdisc_run calls. */
 	do {
-		while (some_qdisc_is_running(dev, 0))
+		while (some_qdisc_is_busy(dev, 0))
 			yield();

 		/*
 		 * Double-check inside queue lock to ensure that all effects
 		 * of the queue run are visible when we return.
 		 */
-		running = some_qdisc_is_running(dev, 1);
+		running = some_qdisc_is_busy(dev, 1);

 		/*
 		 * The running flag should never be set at this point because
--
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