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

[Ingo Molnar <mingo@elte.hu>]

* 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);