From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752708AbbHMOJu (ORCPT ); Thu, 13 Aug 2015 10:09:50 -0400 Received: from mx2.suse.de ([195.135.220.15]:40583 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752079AbbHMOJf (ORCPT ); Thu, 13 Aug 2015 10:09:35 -0400 Date: Thu, 13 Aug 2015 16:09:29 +0200 From: Jan Kara To: Oleg Nesterov Cc: Jan Kara , Al Viro , Dave Chinner , Dave Hansen , "Paul E. McKenney" , Peter Zijlstra , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 7/8] shift percpu_counter_destroy() into destroy_super_work() Message-ID: <20150813140929.GA4392@quack.suse.cz> References: <20150811170343.GA26881@redhat.com> <20150811170416.GA26931@redhat.com> <20150813103518.GG26599@quack.suse.cz> <20150813133616.GC15609@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150813133616.GC15609@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 13-08-15 15:36:16, Oleg Nesterov wrote: > On 08/13, Jan Kara wrote: > > > > On Tue 11-08-15 19:04:16, Oleg Nesterov wrote: > > > > > > So this is just the temporary kludge which helps us to avoid the > > > conflicts with the changes which will be (hopefully) routed via > > > rcu tree. > > > > > > Signed-off-by: Oleg Nesterov > > > > Looking into this again, it would seem somewhat cleaner to me to move the > > destruction to deactivate_locked_super() instead. > > Heh ;) You know, I was looking at deactivate_locked_super(). However, I > simply do not understand this code enough, I failed to verify it would > be safe to destroy s_writers there. Yes, it will be safe. After ->kill_sb() callback the filesystem is dead. There can be someone still holding reference to superblock but these are just users inspecting the structure definitely not caring about freeze protection. > And. Please note destroy_super() in alloc_super() error path, so this > needs a bit more changes in any case. Yes. But you can sleep in alloc_super() so that would be easy enough. > Can't we live with this hack for now? To remind, it will be reverted > (at least partially) in any case. Yes, yes, it is very ugly and the > changelog documents this fact. But it looks simple and safe. To me > it would be better to make the conversion first, then cleanup this > horror after another discussion. All I care about is that long-term, all handling from destroy_super() that needs to sleep ends up in one place. So if you promise you'll make this happen I can live with the workqueue solution for now (but you have to convince also Al as a maintainer ;). Honza -- Jan Kara SUSE Labs, CR