Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case

From	Nikita Yushchenko <nyushchenko@dev.rtsoft.ru>
Newsgroups	linux.kernel
Subject	Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case
Date	2015-11-28 12:20 +0100
Message-ID	<qzLHQ-8cc-17@gated-at.bofh.it> (permalink)
References	(4 earlier) <qxYJc-1N0-7@gated-at.bofh.it> <qxYJc-1N0-9@gated-at.bofh.it> <qxZ2y-29g-13@gated-at.bofh.it> <qynez-130-33@gated-at.bofh.it> <qynRh-1yb-43@gated-at.bofh.it>
Organization	RTSoft Software Development Center

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>> Not sure I understand logic behind this. With the current code,
>> resulting cpu_possible_mask depends on CONFIG_SMP_ON_UP:
>> - if it is set, cpu_possible_mask contains (0 1), as initialized in
>> arm_dt_init_cpu_maps()
>> - if it is not set, cpu_possible_mask contains (0), since
>> imx_smp_init_cpus() removes 1 from there.
> 
> Right, adding debug to arch/arm/kernel/setup.c, just before the
> "if (is_smp())" shows:
> 
> is_smp() 0 possible 3 present 1 online 1
> 
> which is totally wrong: if is_smp() is false, we should not be setting
> up any possible CPUs.  See a patch below to fix that.
> 
> However, this doesn't matter much, because the code in setup.c won't
> initialise the SMP operations struct ...

But cpu start code is not the only place in the kernel that uses cpu_present_mask.

Are you sure that running with invalid cpu_present_mask has no side effects?

> Here's the patch to fix the DT code, which should not be setting
> present CPUs when is_smp() is false.

I see that this fixes the issue as well.

But I still don't understand rationale behind all these is_smp() checks.
This makes init sequence different with and without CONFIG_SMP_ON_UP.
Isn't kernel intended to run ok without CONFIG_SMP_ON_UP?

And if yes - then why not run the same init sequence in both cases?
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Thread

[RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case nyushchenko@dev.rtsoft.ru - 2015-11-23 13:00 +0100
  Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:10 +0100
    Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 13:20 +0100
      Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:50 +0100
    Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 13:20 +0100
    Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Vladimir Murzin <vladimir.murzin@arm.com> - 2015-11-23 13:40 +0100
      Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:50 +0100
        Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 14:10 +0100
          Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-24 16:00 +0100
            Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-24 16:10 +0100
              Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-24 16:30 +0100
            Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-24 16:40 +0100
              Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-28 12:20 +0100
                Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-30 09:30 +0100
      Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Nikita Yushchenko <nyushchenko@dev.rtsoft.ru> - 2015-11-23 13:50 +0100
  Re: [RFC/PATCH] arm: do not skip SMP init calls on SMP_ON_UP case Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-23 13:10 +0100

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