Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759221Ab2J2OGs (ORCPT ); Mon, 29 Oct 2012 10:06:48 -0400 Received: from mx2.parallels.com ([64.131.90.16]:37064 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757268Ab2J2OGq (ORCPT ); Mon, 29 Oct 2012 10:06:46 -0400 Message-ID: <508E8D6A.5040602@parallels.com> Date: Mon, 29 Oct 2012 18:06:34 +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: Michal Hocko CC: , , , Andrew Morton , Tejun Heo , Li Zefan , Johannes Weiner , KAMEZAWA Hiroyuki , Balbir Singh Subject: Re: [PATCH v3 4/6] cgroups: forbid pre_destroy callback to fail References: <1351251453-6140-1-git-send-email-mhocko@suse.cz> <1351251453-6140-5-git-send-email-mhocko@suse.cz> <508E8CDE.1090702@parallels.com> In-Reply-To: <508E8CDE.1090702@parallels.com> 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: 1509 Lines: 36 On 10/29/2012 06:04 PM, Glauber Costa wrote: > On 10/26/2012 03:37 PM, Michal Hocko wrote: >> Now that mem_cgroup_pre_destroy callback doesn't fail (other than a race >> with a task attach resp. child group appears) finally we can safely move >> on and forbit all the callbacks to fail. >> The last missing piece is moving cgroup_call_pre_destroy after >> cgroup_clear_css_refs so that css_tryget fails so no new charges for the >> memcg can happen. >> We cannot, however, move cgroup_call_pre_destroy right after because we >> cannot call mem_cgroup_pre_destroy with the cgroup_lock held (see >> 3fa59dfb cgroup: fix potential deadlock in pre_destroy) so we have to >> move it after the lock is released. >> > > If we don't have the cgroup lock held, how safe is the following > statement in mem_cgroup_reparent_charges(): > > if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children)) > return -EBUSY; > > ? > > IIUC, although this is not generally safe, but it would be safe here > because at this point we are expected to had already set the removed bit > in the css. If this is the case, however, this condition is impossible > and becomes useless - in which case you may want to remove it from Patch1. > Which I just saw you doing in patch5... =) -- 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/