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 9AA09C43215 for ; Fri, 15 Nov 2019 17:48:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 757592073C for ; Fri, 15 Nov 2019 17:48:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573840129; bh=Cec4G7J1NLFbLK/mgcOgF4kBUaE1PEQX0oi24K30Wo8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=UrZTjTi35C2u72gH2M5TNHrhOhssPoxr+4yBI/pvhBRtUL/cTRKJZW/DIjEWyvVrs x9vuN48ml5AhZvvCFuCrjJq7Fl/x5p35t4mDEetpwJ88bOOC7mKbsTychPooZRZ65L QKc/YlEAL5EM4HqfUfuWJUGI+onuWeAZVOscv87o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726131AbfKORss (ORCPT ); Fri, 15 Nov 2019 12:48:48 -0500 Received: from mail-qv1-f53.google.com ([209.85.219.53]:44857 "EHLO mail-qv1-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725848AbfKORss (ORCPT ); Fri, 15 Nov 2019 12:48:48 -0500 Received: by mail-qv1-f53.google.com with SMTP id d3so4078334qvs.11; Fri, 15 Nov 2019 09:48:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Tggz0Sup0tJF7r/miqRqPkt8QctjM6InW2y0Q0myCrA=; b=YRwOG6FnZpiAU/ObEKfFoLeH/BCO4X7fGLIUL0/xug+uGlbhVwQmRJuMAs4JwqSmdZ BBBEcHVid4mj6iyuE2y9bFo3+ursRhOY8/ugAfoZFQOoTb8BU2o41wtkDGZRfiXZTPS/ 5rFKFXg/Hq4c9Vbva7CFLkNwlT4AP/YwWMy+6RKbbruhfMkZTxjjQU7lMB2MIzdEEqZC kFoApnlFJS+sKduvaKlGXvm/TzT3TC4W6Pyryv8bXo+kOCLHqkOz7mDgBfRofD4ICoaD /bx/hfTcEsEURtRGNZVn3tUY9m193AYhL5Jea7wkggKhwjlM3APZflaFfE9HJXCM6D0B m94A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=Tggz0Sup0tJF7r/miqRqPkt8QctjM6InW2y0Q0myCrA=; b=WEgISatshGoj4JR6Xu4Y57uolSISy6nVdxuUapaC5pLUbbSh0UDMOqnrkAddHCzb3E DuZ8zJIem3v+hVn3K9OikqdHzuNHj5LBExaXMDZTsgCjslNDeCUvJORD8c+3J2naD195 EFzze6fnkoFrTf5FHEY/E1doeiyEdXIxa8FWmVq1SV/6zKCtrJUW+PxRdwLeFfYWFtqQ Zea2dnrOZlre/CwKuK98/DijUn6MiOhyF0bVOSlrtZ2iBhmZayInqxDBHZkl8YpubguX 1IEl5Q1yDV+B1fo9XViaoyzWy/6t+JVaP+qlg/AY1PswCtC24cSgpjTKIV0RI2bDbMxE Q6pA== X-Gm-Message-State: APjAAAXUCblhF6NU4X7SlSwLDpLTGkuoFllE50Sj3uebkgsR/VGZFyTY zCHTGhTtCm26oiWQXzUG2T8= X-Google-Smtp-Source: APXvYqydPSTYxYN82kZIJOLGlcFhkq+6JEEBk7LqqlPn79KmDLe7cS/rHfO/ZD0Ur8OF3MNkOiR1lA== X-Received: by 2002:ad4:458b:: with SMTP id x11mr7704350qvu.7.1573840127172; Fri, 15 Nov 2019 09:48:47 -0800 (PST) Received: from localhost ([2620:10d:c091:480::4ef1]) by smtp.gmail.com with ESMTPSA id 76sm4642961qke.111.2019.11.15.09.48.46 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 15 Nov 2019 09:48:46 -0800 (PST) Date: Fri, 15 Nov 2019 09:48:44 -0800 From: Tejun Heo To: Michal Hocko 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: <20191115174844.GR4163745@devbig004.ftw2.facebook.com> 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> <20191114193340.GA24848@dhcp22.suse.cz> <20191114193736.GL4163745@devbig004.ftw2.facebook.com> <20191115174031.GA15216@dhcp22.suse.cz> <20191115174721.GB15216@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191115174721.GB15216@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, Nov 15, 2019 at 06:47:21PM +0100, Michal Hocko wrote: > s@online@offline@ > > And reading after myself it turned out to sound differently than I > meant. What I wanted to say really is, what is the difference that > css_tryget_online really guarantee when the css might go offline right > after the call suceeds so more specifically what is the difference > between > if (css_tryget()) { > if (online) > DO_SOMETHING > } > and > if (css_tryget_online()) { > DO_SOMETHING > } > > both of them are racy and do not provide any guarantee wrt. online > state. It's about not giving new reference when the object is known to be delted to the user. Can you please think more about how file deletions work? Thanks. -- tejun