linux-kernel - Re: [PATCH] x86: Document the hotplug code is incompatible with x86 irq handling

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Date:	Thu, 31 May 2007 08:34:28 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, Neil Brown <neilb@...e.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...e.hu>,
	Zwane Mwaikambo <zwane@...uxpower.ca>
Subject: Re: [PATCH] x86: Document the hotplug code is incompatible with x86
 irq handling

Eric W. Biederman wrote:
> I just realized that except for doing the code review and noticing
> that the current cpu hotplug code is fundamentally incompatible
> with x86 I haven't done anything about it.  So here is my patch
> to document what is wrong.
> 
> The current cpu hotplug code requires irqs to be migrated from a cpu
> outside of irq context.  On x86 ioapics simply do not support this,
> making the code unfixable without major redesign of the generic cpu
> hotplug code.
> 
> So this patch makes CPU_HOTPLUG on x86 depend on CONFIG_BROKEN
> and adds a WARN_ON so people that do enable it are not in doubt about
> which part of the code is broken, even if it does work for them.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>

I don't think this is useful, though the code may be problematic, this 
patch will break suspend on all SMP machines with an existing config, 
which is a major regression..

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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