From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mundt Subject: Re: [Ksummit-2010-discuss] [v2] Remaining BKL users, what to do Date: Tue, 19 Oct 2010 22:54:46 +0900 Message-ID: <20101019135445.GA19367@linux-sh.org> References: <201009161632.59210.arnd@arndb.de> <201010190926.54635.arnd@arndb.de> <1287491998.16971.360.camel@gandalf.stny.rr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Arnd Bergmann , Dave Airlie , Theodore Kilgore , Greg KH , codalist@telemann.coda.cs.cmu.edu, autofs@linux.kernel.org, Samuel Ortiz , Jan Kara , Mikulas Patocka , Jan Harkes , netdev@vger.kernel.org, Anders Larsen , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Bryan Schumaker , Christoph Hellwig , ksummit-2010-discuss@lists.linux-foundation.org, Petr Vandrovec , Arnaldo Carvalho de Melo , linux-fsdevel@vger.kernel.org, Evgeniy Dushistov , Ingo Molnar , Andrew Hendry , linux-media@vger.kernel.org To: Steven Rostedt Return-path: Content-Disposition: inline In-Reply-To: <1287491998.16971.360.camel@gandalf.stny.rr.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Oct 19, 2010 at 08:39:58AM -0400, Steven Rostedt wrote: > On Tue, 2010-10-19 at 09:26 +0200, Arnd Bergmann wrote: > > 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. > > I think we also need to cover the PREEMPT case too. But that could be a > compile time check, since you can't boot a preempt kernel and make it > non preempt. > There are enough nameless embedded vendors that have turned a preempt kernel in to a non-preempt one at run-time by leaking the preempt count, whether by design or not, so it's certainly possile :-)