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

[Mark Hounschell <markh@compro.net>]

Ingo Molnar wrote:
> * 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);
> 

I'm trying that right this moment. It may take a while before I know if
it helps.

Mark