From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753417AbdEPSCa (ORCPT ); Tue, 16 May 2017 14:02:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:46151 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752589AbdEPSCY (ORCPT ); Tue, 16 May 2017 14:02:24 -0400 Date: Tue, 16 May 2017 20:02:17 +0200 From: "Luis R. Rodriguez" To: "Luis R. Rodriguez" Cc: Petr Mladek , Kees Cook , Peter Zijlstra , shuah@kernel.org, Jessica Yu , Rusty Russell , "Eric W. Biederman" , Dmitry Torokhov , Arnaldo Carvalho de Melo , Jonathan Corbet , martin.wilck@suse.com, Michal Marek , hare@suse.com, rwright@hpe.com, Jeff Mahoney , DSterba@suse.com, fdmanana@suse.com, neilb@suse.com, Guenter Roeck , rgoldwyn@suse.com, subashab@codeaurora.org, Heinrich Schuchardt , Aaron Tomlin , mbenes@suse.cz, "Paul E. McKenney" , Dan Williams , Josh Poimboeuf , "David S. Miller" , Ingo Molnar , Andrew Morton , Linus Torvalds , linux-kselftest@vger.kernel.org, "linux-doc@vger.kernel.org" , LKML Subject: Re: [RFC 04/10] kmod: provide wrappers for kmod_concurrent inc/dec Message-ID: <20170516180217.GG17314@wotan.suse.de> References: <20161208184801.1689-1-mcgrof@kernel.org> <20161208194824.2532-1-mcgrof@kernel.org> <20161208210859.GZ1402@wotan.suse.de> <20161215124625.GA14324@pathway.suse.cz> <20161216080500.GE13946@wotan.suse.de> <20170110185710.GG13946@wotan.suse.de> <20170111200857.GR13946@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170111200857.GR13946@wotan.suse.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 11, 2017 at 09:08:57PM +0100, Luis R. Rodriguez wrote: > On Tue, Jan 10, 2017 at 07:57:10PM +0100, Luis R. Rodriguez wrote: > > On Fri, Dec 16, 2016 at 09:05:00AM +0100, Luis R. Rodriguez wrote: > > > On Thu, Dec 15, 2016 at 01:46:25PM +0100, Petr Mladek wrote: > > > > On Thu 2016-12-08 22:08:59, Luis R. Rodriguez wrote: > > > > > On Thu, Dec 08, 2016 at 12:29:42PM -0800, Kees Cook wrote: > > > > > > On Thu, Dec 8, 2016 at 11:48 AM, Luis R. Rodriguez wrote: > > > > > > > + if (atomic_read(&kmod_concurrent) < max_modprobes) > > > > > > > + return 0; > > > > > > > + atomic_dec(&kmod_concurrent); > > > > > > > + return -ENOMEM; > > > > > > > +} > > > > > > > + > > > > > > > +static void kmod_umh_threads_put(void) > > > > > > > +{ > > > > > > > + atomic_dec(&kmod_concurrent); > > > > > > > +} > > > > > > > > > > > > Can you use a kref here instead? We're trying to kill raw use of > > > > > > atomic_t for reference counting... > > > > > > > > > > That's a much broader functional change than I was looking for, but I am up for > > > > > it. Can you describe the benefit of using kref you expect or why this is an > > > > > ongoing crusade? Since its a larger functional change how about doing this > > > > > change later, and we can test impact with the tress test driver. In theory if > > > > > there are benefits can't we add a test case to prove the gains? > > > > > > > > Kees probably refers to the kref improvements that Peter Zijlstra > > > > is working on, see > > > > https://lkml.kernel.org/r/20161114174446.832175072@infradead.org > > > > > > > > The advantage is that the new refcount API handles over and > > > > underflow. > > > > > > > > Another advantage is that it increments/decrements the value > > > > only when it is safe. It uses cmpxchg to make sure that > > > > the checks are valid. > > > > > > Great thanks, will look into that. > > > > OK I've done the conversion now, the only thing is linux-next as of today lacks > > KREF_INIT() so I've open coded it for now. Once Peter's changes get merged the > > only thing we'dneed is to change the open code line to KREF_INIT(). > > > > I'll annotate this as Suggested-by Kees and Petr, I did this as a separate atomic > > step after this to make it easier for review. > > Spoke too soon, kref_read() is not upstream yet either, so I can hold conversion > over until Peter's work is merged. Peter please Cc me on those patches if possible > :D All the needed kref stuff is upstream now, however, kref is overkill for kmod_concurrent given this is just a counter, it is not used to release any object, and kref_put() requires such mechanism. The lightweight refcount_t is much more appropriate here so will use that and respin this series, finally. Luis