linux-kernel - Re: regression in 2.6.23-rc8

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Date:	Mon, 01 Oct 2007 21:55:38 +0400
From:	Alexey Starikovskiy <astarikovskiy@...e.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Bill Davidsen <davidsen@....com>, Mark Lord <lkml@....ca>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: regression in 2.6.23-rc8 - power off failed

Rafael J. Wysocki wrote:
> On Saturday, 29 September 2007 22:47, Bill Davidsen wrote:
>> Alexey Starikovskiy wrote:
>>
>>> -static void
>>> -acpi_power_off (void)
>>> -{
>>> -       printk("%s called\n",__FUNCTION__);
>>> -       /* Some SMP machines only can poweroff in boot CPU */
>>> -       set_cpus_allowed(current, cpumask_of_cpu(0));
>>> ACPI in kernel 2.6.12 did disable non-boot cpus too in powe_off.
>>> Later only comment was left for some reason...
>>>
>> Am I midreading that code, or does it really assume that the boot cpu is 
>> always zero? Or just that zero will be able to do the power off?
>>
>> In any case I have had an SMP machine which did not have a CPU zero, and 
>> it was discussed here, I believe. Wonder what happens if you set 
>> affinity to a CPU you don't have...
> 
> Good question, but it also caused other problems to appear, IIRC.
> 
> IMHO, it's better to call disable_nonboot_cpus() in an appropriate place
> anyway.
> 
> Greetings,
> Rafael
Ok, here is commit which removed the code in question from acpi_power_off:

commit 6660316cb7a1a2c59a73a52870490c0f782f45c1
Author: Eric W. Biederman <ebiederm@...ssion.com>
Date:   Tue Jul 26 12:16:00 2005 -0600

    [PATCH] acpi_power_off: Don't switch to the boot cpu

    machine_power_off on i386 and x86_64 now switch to the
    boot cpu out of paranoia and because the MP Specification indicates it
    is a good idea on reboot, so for those architectures it is a noop.
    I can't see anything in the acpi spec that requires you to be on
    the boot cpu to power off the system, so this should not be an issue
    for ia64.  In addition ia64 has the altix a massive multi-node
    system where switching to the boot cpu sounds insane as we may
    hot removed the boot cpu.

    Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
    Signed-off-by: Linus Torvalds <torvalds@...l.org>

Regards,
Alex.
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