Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422887Ab2JaNmo (ORCPT ); Wed, 31 Oct 2012 09:42:44 -0400 Received: from mx2.parallels.com ([64.131.90.16]:47677 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933628Ab2JaNmk (ORCPT ); Wed, 31 Oct 2012 09:42:40 -0400 Message-ID: <50912AC1.508@parallels.com> Date: Wed, 31 Oct 2012 17:42:25 +0400 From: Glauber Costa User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121016 Thunderbird/16.0.1 MIME-Version: 1.0 To: Tejun Heo CC: , , , , , , , Subject: Re: [PATCH 4/8] cgroup: deactivate CSS's and mark cgroup dead before invoking ->pre_destroy() References: <1351657365-25055-1-git-send-email-tj@kernel.org> <1351657365-25055-5-git-send-email-tj@kernel.org> In-Reply-To: <1351657365-25055-5-git-send-email-tj@kernel.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1235 Lines: 32 On 10/31/2012 08:22 AM, Tejun Heo wrote: > Because ->pre_destroy() could fail and can't be called under > cgroup_mutex, cgroup destruction did something very ugly. > > 1. Grab cgroup_mutex and verify it can be destroyed; fail otherwise. > > 2. Release cgroup_mutex and call ->pre_destroy(). > > 3. Re-grab cgroup_mutex and verify it can still be destroyed; fail > otherwise. > > 4. Continue destroying. > > In addition to being ugly, it has been always broken in various ways. > For example, memcg ->pre_destroy() expects the cgroup to be inactive > after it's done but tasks can be attached and detached between #2 and > #3 and the conditions that memcg verified in ->pre_destroy() might no > longer hold by the time control reaches #3. > > Now that ->pre_destroy() is no longer allowed to fail. We can switch > to the following. > > 1. Grab cgroup_mutex and fail if it can't be destroyed; fail > otherwise. > fail, or fail otherwise? Seems quite negative =) -- 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/