From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030936AbXDPUKV (ORCPT ); Mon, 16 Apr 2007 16:10:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030937AbXDPUKV (ORCPT ); Mon, 16 Apr 2007 16:10:21 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:51346 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030936AbXDPUKT (ORCPT ); Mon, 16 Apr 2007 16:10:19 -0400 Date: Mon, 16 Apr 2007 12:11:20 -0700 From: Greg KH To: Dmitry Torokhov Cc: Cornelia Huck , linux-kernel , Alan Stern , Tejun Heo , Rusty Russell Subject: Re: [Patch -mm 0/3] RFC: module unloading vs. release function Message-ID: <20070416191120.GA15490@kroah.com> References: <20070416193619.4659a847@gondolin.boeblingen.de.ibm.com> <20070416184716.GA6262@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.14 (2007-02-12) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 16, 2007 at 03:03:16PM -0400, Dmitry Torokhov wrote: > On 4/16/07, Greg KH wrote: > >On Mon, Apr 16, 2007 at 02:30:17PM -0400, Dmitry Torokhov wrote: > >> On 4/16/07, Cornelia Huck wrote: > >> >Hi, > >> > > >> >based on the discussion in "How should an exit routine wait for > >> >release() callbacks?", I've cooked up some patches that make module > >> >unload wait until the last reference for a kobject has been dropped. > >> >This should plug the "release function in already deleted module" race; > >> >however, if the last kobject_put() from the module containing the > >> >release function is not in the module's exit function, there's still a > >> >small window (not sure if and how to plug this). > >> > >> Unfortunately all this "wait for refcount in module's exit" schemas > >> lead to the following deadlock: > >> > >> rmmod my_module < /path/to/some/file/incrementing/my/refcount > > > >No, it should just return "module in use" as the reference count it > >grabbed before rmmod is called. > > > > No, because it it were module's refcount we woudl not have problem > with ->release() to begin with. It is object's refcount. Yes, but with these patches, we are incrementing that reference count when the kobject is created, which will cause this to fail. > >But either way, that's just foolish to try to prevent that from failing > >:) > > Why? It works now for most of teh subsystems. That's because it is buggy :) thanks, greg k-h