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Date: Thu, 14 Aug 2008 07:59:07 +0000
From: Jarek Poplawski <jarkao2@...il.com>
To: David Miller <davem@...emloft.net>
Cc: herbert@...dor.apana.org.au, netdev@...r.kernel.org
Subject: Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl_lock().
On Wed, Aug 13, 2008 at 03:19:18PM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Wed, 13 Aug 2008 10:50:52 +0000
>
> > On Wed, Aug 13, 2008 at 08:42:38PM +1000, Herbert Xu wrote:
> > > On Wed, Aug 13, 2008 at 10:27:01AM +0000, Jarek Poplawski wrote:
> > > >
> > > > - in net_tx_action() we can hit a place just after clear_bit() where
> > > > none of these bits is set. Of course, hitting this 2 times in a row
> > > > seems to be very unprobable, yet possible, and a lock isn't helpful
> > > > here, so probably some change around this would make this nicer.
> > > >
> > > > - isn't there possible some longer ping-pong between qdic_run() and
> > > > net_tx_action() when dev_requeue_skb() would get it back to
> > > > __netif_schedule() and so on (with NETDEV_TX_BUSY)?
> > >
> > > Good point. I think we should add an aliveness check in both
> > > net_tx_action and qdisc_run. In fact the net_tx_action problem
> > > existed previously as well. But it is pretty darn unlikely.
> >
> > Yes, it seems qdisc_reset() doesn't have to help with this, so
> > probably there is needed some requeue counter or something...
>
> Ok, so what I'm going to do is check in my patch and then try
> to figure out how to resolve this "both bits clear" scenerio.
Here is my proposal.
Jarek P.
----------->
net: Change handling of the __QDISC_STATE_SCHED flag in net_tx_action().
Change handling of the __QDISC_STATE_SCHED flag in net_tx_action() to
enable proper control in dev_deactivate_queue(). Now, if this flag is
seen as unset under root_lock means a qdisc can't be netif_scheduled.
Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
---
net/core/dev.c | 34 +++++++++++++++++++---------------
1 files changed, 19 insertions(+), 15 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 600bb23..f67581b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1339,19 +1339,23 @@ static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
}
-void __netif_schedule(struct Qdisc *q)
+static inline void __netif_reschedule(struct Qdisc *q)
{
- if (!test_and_set_bit(__QDISC_STATE_SCHED, &q->state)) {
- struct softnet_data *sd;
- unsigned long flags;
+ struct softnet_data *sd;
+ unsigned long flags;
- local_irq_save(flags);
- sd = &__get_cpu_var(softnet_data);
- q->next_sched = sd->output_queue;
- sd->output_queue = q;
- raise_softirq_irqoff(NET_TX_SOFTIRQ);
- local_irq_restore(flags);
- }
+ local_irq_save(flags);
+ sd = &__get_cpu_var(softnet_data);
+ q->next_sched = sd->output_queue;
+ sd->output_queue = q;
+ raise_softirq_irqoff(NET_TX_SOFTIRQ);
+ local_irq_restore(flags);
+}
+
+void __netif_schedule(struct Qdisc *q)
+{
+ if (!test_and_set_bit(__QDISC_STATE_SCHED, &q->state))
+ __netif_reschedule(q);
}
EXPORT_SYMBOL(__netif_schedule);
@@ -1974,15 +1978,15 @@ static void net_tx_action(struct softirq_action *h)
head = head->next_sched;
- smp_mb__before_clear_bit();
- clear_bit(__QDISC_STATE_SCHED, &q->state);
-
root_lock = qdisc_lock(q);
if (spin_trylock(root_lock)) {
+ smp_mb__before_clear_bit();
+ clear_bit(__QDISC_STATE_SCHED,
+ &q->state);
qdisc_run(q);
spin_unlock(root_lock);
} else {
- __netif_schedule(q);
+ __netif_reschedule(q);
}
}
}
--
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