Re: Ingo's realtime_preempt patch causes kernel oops

[Steven Rostedt <rostedt@goodmis.org>]

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
 };