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Date: Fri, 16 Jul 2004 15:27:59 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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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?
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Nick Piggin wrote:
> Dave Hansen wrote:
> 
>> On Thu, 2004-07-15 at 20:03, Nick Piggin wrote:
>>
>>> It shouldn't because sched_init sets up dummy domains for
>>> all runqueues.
>>>
>>> Obviously something is going wrong somewhere though.
>>
>>
>>
>> Hmmm, but there still might be some concurrency problems, right?  There
>> isn't any locking while the setup is being done, so are all of the
>> intermediate initialization states valid?  Or, could one of the CPUs be
>> catching the init code in the middle of an operation?
>>
> 
> cpu_attach_domain is supposed to be able to do the switchover
> without any races.

Although the sched_domain_debug is definitely racy. It should really
be locking each runqueue before traversing its domains. Just undef
SCHED_DOMAIN_DEBUG to be sure...