From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 1/8] cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs Date: Wed, 31 Oct 2012 09:41:23 -0700 Message-ID: <20121031164123.GD2945@htj.dyndns.org> References: <1351657365-25055-1-git-send-email-tj@kernel.org> <1351657365-25055-2-git-send-email-tj@kernel.org> <20121031143751.GA22809@dhcp22.suse.cz> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=Zely8lQuDQlP9kDjnJ/FW9hSNRPZ1ZDFczF6q/aD20M=; b=Jk49A92Kz24YtoQiSaPcmX96rU7HLWqADDHAqpUMXSkzfT2ZoytL1uTNRFPPmFyIee Uo8AtGRVxzoeq8sVl9AAVQgidHnzS3xvp+Yr+QrvrnJYN7svrWXc0J5ehkPYk/6r53+V cbE/Oe4iNl6X09ZIi4bFBv9PvomuIAN1VfeCGZS7nBdAovj5fabcJDtuWtQEYFCl5iy+ uzJAlHegRiG4KKhknSYinMhaobUbRWZpDiA8tOcWs69ctptx2sF2kzwuHC+RVb/9SlmV HCY1qU8p9qexHoQ8pXfH+DQXA+VaL6NuUnvz/TRKZ0+yRYVk4UXeb8sy7Qg4NoNcFXys qGxA== Content-Disposition: inline In-Reply-To: <20121031143751.GA22809-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, bsingharora-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Hey, Michal. On Wed, Oct 31, 2012 at 03:37:51PM +0100, Michal Hocko wrote: > > + for_each_subsys(cgrp->root, ss) > > + if (ss->pre_destroy) > > + WARN_ON_ONCE(ss->pre_destroy(cgrp)); > > Hmm, I am not sure I like this WARN_ON_ONCE. First it can happen for > more than one controller and second we can just clear CGRP_WAIT_ON_RMDIR > and return with EBUSY. The only possible failure at the moment is when a > new task or a child group appear. > I know it is not a big deal because it will disappear later in the > series but it would be more readable IMO. The WARN_ON_ONCE() is just moved from the original cgroup_call_pre_destroy(). We can add an error out there but that makes future changes difficult. It's a chicken and egg problem. You gotta break the loop somewhere. Thanks. -- tejun From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933283Ab2JaQla (ORCPT ); Wed, 31 Oct 2012 12:41:30 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:41637 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757694Ab2JaQl2 (ORCPT ); Wed, 31 Oct 2012 12:41:28 -0400 Date: Wed, 31 Oct 2012 09:41:23 -0700 From: Tejun Heo To: Michal Hocko Cc: lizefan@huawei.com, hannes@cmpxchg.org, bsingharora@gmail.com, kamezawa.hiroyu@jp.fujitsu.com, containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/8] cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs Message-ID: <20121031164123.GD2945@htj.dyndns.org> References: <1351657365-25055-1-git-send-email-tj@kernel.org> <1351657365-25055-2-git-send-email-tj@kernel.org> <20121031143751.GA22809@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121031143751.GA22809@dhcp22.suse.cz> 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 Hey, Michal. On Wed, Oct 31, 2012 at 03:37:51PM +0100, Michal Hocko wrote: > > + for_each_subsys(cgrp->root, ss) > > + if (ss->pre_destroy) > > + WARN_ON_ONCE(ss->pre_destroy(cgrp)); > > Hmm, I am not sure I like this WARN_ON_ONCE. First it can happen for > more than one controller and second we can just clear CGRP_WAIT_ON_RMDIR > and return with EBUSY. The only possible failure at the moment is when a > new task or a child group appear. > I know it is not a big deal because it will disappear later in the > series but it would be more readable IMO. The WARN_ON_ONCE() is just moved from the original cgroup_call_pre_destroy(). We can add an error out there but that makes future changes difficult. It's a chicken and egg problem. You gotta break the loop somewhere. Thanks. -- tejun