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Date: Mon, 19 Jul 2004 17:31:33 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Keshavamurthy Anil S <anil.s.keshavamurthy@intel.com>
CC: Dave Hansen <haveblue@us.ibm.com>,
       "Matthew C. Dobson [imap]" <colpatch@us.ibm.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: sched domains bringup race?
References: <1089944026.32312.47.camel@nighthawk> <20040718134559.A25488@unix-os.sc.intel.com>
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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?