Re: Ingo's realtime_preempt patch causes kernel oops

Yann.LEPROVOST
2006-05-23T16:33:22Z

I forgot to say that I let SA_SHIRQ as the IRQ line is shared...
It seems to work correctly...

Yann

Steven Rostedt
<rostedt@goodmis.
org> To
Daniel Walker <dwalker@mvista.com>
23/05/2006 18:02 cc
Yann.LEPROVOST@wavecom.fr,
linux-kernel@vger.kernel.org,
Thomas Gleixner
<tglx@linutronix.de>, Ingo Molnar
<mingo@elte.hu>
Subject
Re: Ingo's realtime_preempt patch
causes kernel oops

On Tue, 2006-05-23 at 08:33 -0700, Daniel Walker wrote:
> On Tue, 2006-05-23 at 10:19 -0400, Steven Rostedt wrote:
>
> >
> > The fault is at 0x40 and looking at profile_tick it calls
> > user_mode(regs). user_mode(x) is defined in arm as
> > (((regs)->ARM_cpsr & 0xf) == 0)
> >
> > And ARM_cpsr is uregs[16] So if arm has 4 byte words and regs was
NULL,
> > it would fault on 16*4 = 64 or 0x40
> >
> > It looks like the timer interrupt on this board is having a NULL regs
> > passed to it when hard interrupts are threads. Which might mean that
> > the timer interrupt is itself a thread.
>
> Hmm, well usually ARM timer interrupts have the SA_TIMER flag .. In
> realtime ARM changes SA_TIMER includes SA_NODELAY ..
>
> In 2.6.17-rc4
>
> arch/arm/mach-at91rm9200/time.c
>
> static struct irqaction at91rm9200_timer_irq = {
> .name = "at91_tick",
> .flags = SA_SHIRQ | SA_INTERRUPT,
> .handler = at91rm9200_timer_interrupt
> };
>
> No SA_TIMER, and no SA_NODELAY , so i'd imagine it's is in a thread ..

Yep, I would say it is.

Yann, could you try the following patch to see if it makes it better for
you. I added SA_NODELAY so that the timer is run in interrupt context,
and removed the shared flag, because I have no idea what might share a
timer interrupt, and it might cause other bugs. If something needs to
share this interrupt, then we need to do something else.

Since I don't have any arm boards, I cant test it, so this wasn't even
compiled.

-- Steve

Index: linux-2.6.16-rt23/arch/arm/mach-at91rm9200/time.c
===================================================================
--- linux-2.6.16-rt23.orig/arch/arm/mach-at91rm9200/time.c
2006-05-23 11:58:21.000000000 -0400
+++ linux-2.6.16-rt23/arch/arm/mach-at91rm9200/time.c 2006-05-23
11:58:45.000000000 -0400
@@ -87,7 +87,7 @@ static irqreturn_t at91rm9200_timer_inte

static struct irqaction at91rm9200_timer_irq = {
.name = "at91_tick",
- .flags = SA_SHIRQ | SA_INTERRUPT,
+ .flags = SA_INTERRUPT | SA_NODELAY,
.handler = at91rm9200_timer_interrupt
};