From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 57C7AC432C3 for ; Thu, 14 Nov 2019 19:33:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 30018206E1 for ; Thu, 14 Nov 2019 19:33:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573760024; bh=+eititFgmWWKqMRh4n9iOgsONeXdzB6YZwq7YTacQxs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=I3Ec8CMAXZ7pXwu4qJa+bilMJOi4GY2nV5aAFjHYDEZooVr6pwbk9UNokWpPZGmEo htrinZ1FiyhFXriBStrUbXcar/Ty1LB0JFyM1ysBemoT7lsaLiH4EhIv+nNO10MosN 1p2Sjdr5S/MN4up5SrZOaMIGifn63n3uK9Feizu0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726491AbfKNTdn (ORCPT ); Thu, 14 Nov 2019 14:33:43 -0500 Received: from mx2.suse.de ([195.135.220.15]:55164 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726444AbfKNTdn (ORCPT ); Thu, 14 Nov 2019 14:33:43 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id D2A13B2AD; Thu, 14 Nov 2019 19:33:41 +0000 (UTC) Date: Thu, 14 Nov 2019 20:33:40 +0100 From: Michal Hocko To: Tejun Heo Cc: Roman Gushchin , Michal =?iso-8859-1?Q?Koutn=FD?= , "linux-mm@kvack.org" , Andrew Morton , Johannes Weiner , "linux-kernel@vger.kernel.org" , Kernel Team , "stable@vger.kernel.org" Subject: Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Message-ID: <20191114193340.GA24848@dhcp22.suse.cz> References: <20191106225131.3543616-1-guro@fb.com> <20191113162934.GF19372@blackbody.suse.cz> <20191113170823.GA12464@castle.DHCP.thefacebook.com> <20191114191657.GN20866@dhcp22.suse.cz> <20191114192018.GJ4163745@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191114192018.GJ4163745@devbig004.ftw2.facebook.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Thu 14-11-19 11:20:18, Tejun Heo wrote: > Hello, > > On Thu, Nov 14, 2019 at 08:16:57PM +0100, Michal Hocko wrote: > > Then what is the point of this function and what about all other users? > > It is useful for controlling admissions of new userspace visible uses > - e.g. a tracepoint shouldn't be allowed to be attached to a cgroup > which has already been deleted. I am not sure I understand. Roman says that the cgroup can get offline right after the function returns. How is "already deleted" different from "just deleted"? I thought that the state is preserved at least while the rcu lock is held but my memory is dim here. > We're just using it too liberally. Can we get a doc update to be explicit about sensible usecases so that others can be dropped accordingly? -- Michal Hocko SUSE Labs