Re: [RFC][PATCH -rt] irqd starvation on SMP by a single process?

Ingo Molnar
2006-05-12T11:56:42Z

* Mark Hounschell <markh@compro.net> wrote:

> Steven Rostedt wrote:
> >
> > On Fri, 12 May 2006, Ingo Molnar wrote:
> >
> >> ah. This actually uncovered a real bug. We were calling __do_softirq()
> >> with interrupts enabled (and being preemptible) - which is certainly
> >> bad.
> >
> > Hmm, I wonder if this is also affecting Mark's problem.
>
> I thought the same thing when I read it??

could you try the patch below?

Ingo

----

* Steven Rostedt <rostedt@goodmis.org> wrote:

> > one solution would be to forbid disable_irq() from softirq contexts, and
> > to convert the vortex timeout function to a workqueue and use the
> > *_delayed_work() APIs to drive it - and cross fingers there's not many
> > places to fix.
>
> I prefer the above. Maybe even add a WARN_ON(in_softirq()) in
> disable_irq.
>
> But I must admit, I wouldn't know how to make that change without
> spending more time on it then I have for this.

the simplest fix for now would be to use the _nosync variant in the
vortex timeout function.

Mark, does this fix the problem?

Ingo

Index: linux-rt.q/drivers/net/3c59x.c
===================================================================
--- linux-rt.q.orig/drivers/net/3c59x.c
+++ linux-rt.q/drivers/net/3c59x.c
@@ -1897,7 +1897,8 @@ vortex_timer(unsigned long data)

if (vp->medialock)
goto leave_media_alone;
- disable_irq(dev->irq);
+ /* hack! */
+ disable_irq_nosync(dev->irq);
old_window = ioread16(ioaddr + EL3_CMD) >> 13;
EL3WINDOW(4);
media_status = ioread16(ioaddr + Wn4_Media);