From: Herbert Xu

Date: Wed, 13 Aug 2008 14:30:19 +1000
> David Miller  wrote:

quoted text
> >

> > The qdisc pointer traverses to the softirq handler, which can be run

> > in a process context (via ksoftirqd), and this pointer gets there

> > via the per-cpu ->output_queue.

>

> Here are two possible solutions:

>

> 1) The active way: smp_call_function and forcibly remove the qdiscs

> in question from each output_queue.

>

> 2) The passive way: Make dev_deactive call yield() until no qdisc's

> are on an output_queue.  This assumes there is some sort of dead

> flag detection on the output_queue side so it doesn't keep going

> forever.

Yes, we'll need some kind of dead flag it seems.
Another thing we can do is, in the yield loop, grabbing the

__QDISC_STATE_RUNNING bit.
But actually, I think Jarek has a point.
The existing loop there in dev_deactivate() should work _iff_ we make

it look at the proper qdisc.
This is another case where I didn't transform things correctly.  The

old code worked on dev->state since that's where we kept what used

to be __LINK_STATE_QDISC_RUNNING.
But now that state is kept in the qdisc itself.  But we just zapped

the active qdisc, so the old one is in ->qdisc_sleeping not ->qdisc.
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?
Hmmm... maybe we have to sample __QDISC_STATE_SCHED too.
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