linux-kernel - Re: [RFC patch 08/18] cnt32_to_63 should use smp

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Message-Id: <20081107092643.0bd9bb4e.akpm@linux-foundation.org>
Date:	Fri, 7 Nov 2008 09:26:43 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Howells <dhowells@...hat.com>
Cc:	Nicolas Pitre <nico@....org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
	benh@...nel.crashing.org, paulus@...ba.org,
	David Miller <davem@...emloft.net>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-arch@...r.kernel.org
Subject: Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb()

On Fri, 07 Nov 2008 17:10:00 +0000 David Howells <dhowells@...hat.com> wrote:

> 
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > I'd expect it to behave in the same way as it would if the function was
> > implemented out-of-line.
> > 
> > But it occurs to me that the modrobe-doesnt-work thing would happen if
> > the function _is_ inlined anyway, so we won't be doing that.
> > 
> > Whatever.  Killing this many puppies because gcc may do something so
> > bizarrely wrong isn't justifiable.
> 
> With gcc, you get one instance of the static variable from inside a static
> (inline or outofline) function per .o file that invokes it, and these do not
> merge even though they're common symbols.  I asked around and the opinion
> seems to be that this is correct C.  I suppose it's the equivalent of cutting
> and pasting a function between several files - why should the compiler assume
> it's the same function in each?
> 

OK, thanks, I guess that makes sense.  For static inline.  I wonder if
`extern inline' or plain old `inline' should change it.

It's one of those things I hope I never need to know about, but perhaps
we do somewhere have static storage in an inline.  Wouldn't surprise
me, and I bet that if we do, it's a bug.
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