linux-kernel - Re: [Ksummit-2010-discuss] [v2] Remaining BKL users, what to do

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Message-Id: <201010190926.54635.arnd@arndb.de>
Date:	Tue, 19 Oct 2010 09:26:54 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Dave Airlie <airlied@...il.com>
Cc:	Theodore Kilgore <kilgota@...ach.math.auburn.edu>,
	Steven Rostedt <rostedt@...dmis.org>, Greg KH <greg@...ah.com>,
	codalist@...emann.coda.cs.cmu.edu, autofs@...ux.kernel.org,
	Samuel Ortiz <samuel@...tiz.org>, Jan Kara <jack@...e.cz>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Jan Harkes <jaharkes@...cmu.edu>, netdev@...r.kernel.org,
	Anders Larsen <al@...rsen.net>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	Bryan Schumaker <bjschuma@...app.com>,
	Christoph Hellwig <hch@...radead.org>,
	ksummit-2010-discuss@...ts.linux-foundation.org,
	Petr Vandrovec <vandrove@...cvut.cz>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-fsdevel@...r.kernel.org,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Hendry <andrew.hendry@...il.com>,
	linux-media@...r.kernel.org
Subject: Re: [Ksummit-2010-discuss] [v2] Remaining BKL users, what to do

On Tuesday 19 October 2010 06:52:32 Dave Airlie wrote:
> > I might be able to find some hardware still lying around here that uses an
> > i810. Not sure unless I go hunting it. But I get the impression that if
> > the kernel is a single-CPU kernel there is not any problem anyway? Don't
> > distros offer a non-smp kernel as an installation option in case the user
> > needs it? So in reality how big a problem is this?
> 
> Not anymore, which is my old point of making a fuss. Nowadays in the
> modern distro world, we supply a single kernel that can at runtime
> decide if its running on SMP or UP and rewrite the text section
> appropriately with locks etc. Its like magic, and something like
> marking drivers as BROKEN_ON_SMP at compile time is really wrong when
> what you want now is a runtime warning if someone tries to hotplug a
> CPU with a known iffy driver loaded or if someone tries to load the
> driver when we are already in SMP mode.

We could make the driver run-time non-SMP by adding

	if (num_present_cpus() > 1) {
		pr_err("i810 no longer supports SMP\n");
		return -EINVAL;
	}

to the init function. That would cover the vast majority of the
users of i810 hardware, I guess.

	Arnd
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