On Tue, Aug 12, 2008 at 11:16:33PM -0700, David Miller wrote:

quoted text
> From: Jarek Poplawski

> Date: Wed, 13 Aug 2008 06:13:17 +0000

>

> > On Tue, Aug 12, 2008 at 10:11:03PM -0700, David Miller wrote:

> > > So, just like one of Jarek's patches, we should simply change

> > > dev_queue->qdisc into dev_queue->qdisc_sleeping and that should

> > > take care of the bulk of the issues.

> > >

> > > Shouldn't it?

> >

> > If we don't change anything in __netif_schedule() I doubt it's enough.

> > And if this old way of waiting for "outstanding qdisc-less" calls was

> > really needed we should probably wait for both qdisc and qdisc_sleeping

> > then.

>

> I think if we check both RUNNING and SCHED bits, we'll be OK.

>

> > > Hmmm... maybe we have to sample __QDISC_STATE_SCHED too.

> >

> > We could probably even think of using this flag napi_disable() way.

>

> Here (in dev_deactivate), ->qdisc is going to now be &noop_qdisc or

> similar.  Asynchronous contexts can run into that thing as much as

> they want :-)

Thats why I still think a "common" RCU with rcu_dereference() (from

dev_queue pointer) in net_tx_action() should be enough: after

synchronize_rcu() in dev_deactivate() we are sure any qdisc_run(),

from dev_queue_xmit() or net_tx_action() can only see and lock

noop_qdisc. Any activities on qdisc_sleeping can't happen so no

need to wait for this. There could be some skbs enqueued just before

synchronize, and they could be ->reset() and ->destroy() just after,

even without rcu_call().
Otherwise, I think you would better send some code example with these

flags, so we could be sure there is no misunderstanding around this.
Jarek P.

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