Re: Realtime Preemption, 2.6.12, Beginners Guide?

[Alistair John Strachan <s0348365@sms.ed.ac.uk>]

On Thursday 07 Jul 2005 12:42, Ingo Molnar wrote:
> * Alistair John Strachan <s0348365@sms.ed.ac.uk> wrote:
> > > do you have DEBUG_STACKOVERFLOW and latency tracing still enabled?  The
> > > combination of those two options is pretty good at detecting stack
> > > overflows. Also, you might want to enable CONFIG_4KSTACKS, that too
> > > disturbs the stack layout enough so that the error message may make it
> > > to the console.
> >
> > I already have 4KSTACKS on. Latency tracing is enabled, but
> > STACKOVERFLOW isn't; I'll just reenable everything again until we fix
> > this. Do you think if I removed the printk() line I might get some
> > useful information, before it does the stack trace?
>
> usually such loops happen if the stack has been overflown and critical
> information that lies on the bottom of the stack (struct thread_info) is
> overwritten. Then we often cannot even perform simple printks. Stack
> overflow debugging wont prevent the crash, but might give a better
> traceback.

Well, just to let others who have this problem know, it's clear that Ingo's 
rt-preempt patches increase stack pressure on systems (like mine) where stack 
is borderline under 4K by default.

If you disable CONFIG_4KSTACKS the stack overflows seem to disappear. As a 
result, until we isolate the problem, it'd probably be better if Ingo 
maintained an 8K stacks option in the rt-preempt patches assuming Adrian 
Bunk's "kill !4KSTACKS" patch gets into mainline..

-- 
Cheers,
Alistair.

personal:   alistair()devzero!co!uk
university: s0348365()sms!ed!ac!uk
student:    CS/CSim Undergraduate
contact:    1F2 55 South Clerk Street,
            Edinburgh. EH8 9PP.
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