Subject: Re: [patch] i386/x86_64: smp_call_function locking inconsistency
From: Jan Glauber <jan.glauber@de.ibm.com>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David Miller <davem@davemloft.net>, akpm@osdl.org, mingo@elte.hu,
       ak@suse.de, schwidefsky@de.ibm.com, linux-kernel@vger.kernel.org
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	 <20070208.124328.88477956.davem@davemloft.net>
	 <20070209084221.GA8259@osiris.boeblingen.de.ibm.com>
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Date: Fri, 09 Feb 2007 13:57:18 +0100
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On Fri, 2007-02-09 at 09:42 +0100, Heiko Carstens wrote:
> I just want to avoid that s390 has different semantics for
> smp_call_functiom*() than any other architecture. But then again it
> will probably not hurt since we allow more.
> Another thing that comes into my mind is smp_call_function together
> with cpu hotplug. Who is responsible that preemption and with that
> cpu hotplug is disabled?
> Is it the caller or smp_call_function itself?

I think the caller must disable preemption since smp_call_function()
means "do something on all but the current cpu". If the preempt_disable
would happen only in smp_call_function() it could already be running on
a different cpu, which is not what the caller wants.

If preemption must be disabled before smp_call_function() we should have
the same semantics for all smp_call_function_* variants.

Jan

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