Re: sched domains bringup race?

[Nick Piggin]

Keshavamurthy Anil S wrote:
> On Thu, Jul 15, 2004 at 07:13:46PM -0700, Dave Hansen wrote:
>
> > I keep getting oopses for the non-boot CPU in find_busiest_group(). 
> > This occurs the first time that the CPU goes idle.  Those groups are set
> > up in sched_init_smp(), which is called after smp_init():
> >
> > static int init(void * unused)
> > {
> > 	...
> >        fixup_cpu_present_map();
> >        smp_init();
> >        sched_init_smp();
> >
> > But, the idle threads for the secondary CPUs are initialized in
> > smp_init().  So, what happens when a CPU tries to schedule (using sched
> > domains) before sched_init_smp() completes?  I think it goes boom! :)
> >
> > Anyway, I was thinking that we should just hold the runqueue lock on the
> > non-boot CPUs until the sched domain init code is done.  Does that sound
> > feasible?
>
>
> Even on my system which is Intel 865 chipset (P4 with HT enabled system) 
> I see a bug check somewhere in the schedular_tick during boot.
> However if I move the sched_init_smp() after do_basic_setup() the
> kernel boots without any problem. Any clue here?
>
>  static int init(void * unused)
>  {
>  	...
>          fixup_cpu_present_map();
>          smp_init();
> 	 populate_rootfs();
> 	 do_basic_setup();
>  
>          sched_init_smp();

There shouldn't be any problem doing that if we have to, obviously we
need to know why. Is it possible that cpu_sibling_map, or one of the
CPU masks isn't set up correctly at the time of the call?
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