linux-kernel - Re: [PATCH v2] hwmon (coretemp): Fix build breakage if SMP is undefined

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Date:	Mon, 27 Sep 2010 18:00:59 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	Pekka Enberg <penberg@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Jean Delvare <khali@...ux-fr.org>
Subject: Re: [PATCH v2] hwmon (coretemp): Fix build breakage if SMP is undefined

On Mon, Sep 27, 2010 at 5:26 PM, Guenter Roeck
<guenter.roeck@...csson.com> wrote:
>
> Not that simple. cpu_sibling_mask()  is defined in asm/smp.h, which is only
> included from linux/smp.h if SMP is defined. But many other files do include
> asm/smp.h directly. This causes the following error all over the place
> if CONFIG_SMP is not defined.

Yeah, that's broken.  Seriously broken.

And I guess that if you had happened to include <asm/smp.h> in
coretemp.c you would magically have gotten that cpu_sibling_map()
thing, and it would just work - by mistake.

And maybe that's the correct (and really hacky) fix right now. Rather
than introduce an UP-only cpu_sibling_mask(), get the SMP version, and
get it ignored.

Seriously broken, but there it is.

In the long run, I guess we should either
 - disallow naked '<asm/smp.h>' includes
OR
 - just make '<linux/smp.h>' unconditionally include <asm/smp.h>

to at least not have that insane "some things exist in CONFIG_SMP or
not depending on how you include files".

                           Linus
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