linux-kernel - Re: [PATCH v2 17/32] arm: define __smp

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Message-ID: <20160104133658.GY6344@twins.programming.kicks-ass.net>
Date:	Mon, 4 Jan 2016 14:36:58 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	virtualization@...ts.linux-foundation.org,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
	x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	xen-devel@...ts.xenproject.org, Ingo Molnar <mingo@...nel.org>,
	Tony Lindgren <tony@...mide.com>,
	Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH v2 17/32] arm: define __smp_xxx

On Sun, Jan 03, 2016 at 11:12:44AM +0200, Michael S. Tsirkin wrote:
> On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux wrote:

> > My only concern is that it gives people an additional handle onto a
> > "new" set of barriers - just because they're prefixed with __*
> > unfortunately doesn't stop anyone from using it (been there with
> > other arch stuff before.)
> > 
> > I wonder whether we should consider making the smp memory barriers
> > inline functions, so these __smp_xxx() variants can be undef'd
> > afterwards, thereby preventing drivers getting their hands on these
> > new macros?
> 
> That'd be tricky to do cleanly since asm-generic depends on
> ifndef to add generic variants where needed.
> 
> But it would be possible to add a checkpatch test for this.

Wasn't the whole purpose of these things for 'drivers' (namely
virtio/xen hypervisor interaction) to use these?

And I suppose most of virtio would actually be modules, so you cannot do
what I did with preempt_enable_no_resched() either.

But yes, it would be good to limit the use of these things.
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