linux-kernel - Re: [patch] i386/x86_64: smp_call

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Message-Id: <20070208.124328.88477956.davem@davemloft.net>
Date:	Thu, 08 Feb 2007 12:43:28 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	heiko.carstens@...ibm.com
Cc:	akpm@...l.org, mingo@...e.hu, ak@...e.de, jan.glauber@...ibm.com,
	schwidefsky@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [patch] i386/x86_64: smp_call_function locking inconsistency

From: Heiko Carstens <heiko.carstens@...ibm.com>
Date: Thu, 8 Feb 2007 21:32:10 +0100

> So either all spin_lock_bh's should be converted to spin_lock,
> which would limit smp_call_function()/smp_call_function_single()
> to process context & irqs enabled.
> Or the spin_lock's could be converted to spin_lock_bh which would
> make it possible to call these two functions even if in softirq
> context. AFAICS this should be safe.

Sparc64 does not allow smp_call_function() from software interrupts
either.

Same for powerpc, mips, alpha.

IA-64 has the inconsistency you've spotted between smp_call_function()
and smp_call_function_single().

In short, it's a mess :-)

I think it's logically simpler if we disallow smp_call_function*()
from any kind of asynchronous context.  But I'm sure your driver
has a true need for this for some reason.
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