Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 17 Jul 2002 16:30:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 17 Jul 2002 16:30:14 -0400 Received: from dsl-213-023-038-064.arcor-ip.net ([213.23.38.64]:54974 "EHLO starship") by vger.kernel.org with ESMTP id ; Wed, 17 Jul 2002 16:30:13 -0400 Content-Type: text/plain; charset=US-ASCII From: Daniel Phillips To: Roman Zippel Subject: Re: [RFC] new module format Date: Wed, 17 Jul 2002 22:34:35 +0200 X-Mailer: KMail [version 1.3.2] Cc: linux-kernel@vger.kernel.org References: In-Reply-To: MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2483 Lines: 56 On Wednesday 17 July 2002 22:12, Roman Zippel wrote: > Hi, > > On Wed, 17 Jul 2002, Daniel Phillips wrote: > > > > 1. Properly fixing module races: I'm playing with a init/start/stop/exit > > > model, this has the advantage that we can stop anyone from reusing a > > > module and we only have to wait for remaining users to go away until we > > > can safely unload the module. > > > > I'm satisfied that, for filesystems at least, all the module races can be > > solved without adding start/stop, and I will present code in due course. > > The start/stop methods are not needed to fix the races, they allow better > control of the unload process. I'm afraid it must show that I didn't read the previous threads closely enough, but what is the specific benefit supposed to be, if not to address the races? > > However, Rusty tells me there are harder cases than filesystems. At this > > point I'm waiting for a specific example. > > For filesystems it's only simpler because they only have a single entry > point, but the basic problem is always the same. What do you mean by single entry point? Mount? Register_filesystem? Lowlevel activity on a filesystem is certainly not restricted to a single entry point. > We have to protect > against module load/unload and unregister. Without an interface change we > will have to add module owner pointers everywhere and we will see > contention on the unload_lock due to try_inc_mod_count. It makes perfect sense for mount to be able to know which module implements its filesystem. I do not see why updating every mount-like thing in the system is bad, if it's the best interface. It's really hard to see why contention on a slow-path lock is anything to worry about. Anyway, it's not hard to fix the locking model so the lock only covers the transitions of state bits, instead of all of free_module. So, I'm still hoping to hear a substantive reason why the filesystem model can't be applied in general to all forms of modular code. To remind you of the issue: the proposition is that the subsystem in the module is always capable of knowing when the module is quiescent, because it does whatever is necessary to keep track of the users and what they're doing. -- Daniel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/