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, URIBL_BLOCKED,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 A8E1CC432C3 for ; Fri, 22 Nov 2019 08:20:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E3BE20714 for ; Fri, 22 Nov 2019 08:20:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574410807; bh=gK6oJApQdfap1GRmd4jnfOse8hyJ8UGnatmDKIcDr68=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=hgTrqFcVmNajBljUWP/babjS0DQdt7hLxA2pVstnj3q9W0CNCm5c9XdDdJLb4KkY4 JSxpkd2LjGp+AMDq/ugMlavqyC0WRMbDHrVKcyURtEkterFPQWLwhOdxHt6yzbSvMm R64YyDwbtUIMj6WQ/cRzS2b7s9/L+i5epAwqhgQ4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726846AbfKVIUG (ORCPT ); Fri, 22 Nov 2019 03:20:06 -0500 Received: from mail-wr1-f68.google.com ([209.85.221.68]:36618 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726018AbfKVIUG (ORCPT ); Fri, 22 Nov 2019 03:20:06 -0500 Received: by mail-wr1-f68.google.com with SMTP id z3so7519615wru.3; Fri, 22 Nov 2019 00:20:04 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=oPT3v6LUVVcOVXi+g802WzoqdgMO1VqYXbBWJl6TUYI=; b=l8PfjEiBknhJLccXhUb9oQ5ay4+RKcqgUFyDqcQXRpOXr7TajTIEw5PDmUWDTOkuO/ CCYYk0/CFR9C4uNsypVTyYjKmwcJxnC8+WDVV8APMfp7vS2jATvYs2kknrJjy+atxlnx 2QtkYPLn+ttq6pkwqBFpwHMSIYJwF9thDjGGGCC1gdJln0x1iUTqipf0c3E5Lq0eggOY dU6wXYwZ9n6pispuF/A43AXqCQGXUtqaFFO79Hr5lks9JDT+uLE7JgtiJi3nMM2zwfFW sFubgXykJIjS3V/BNnq53knhVienGSi1JbkONV8/YyjpiKu38aI1LG910lT14G1S4AxR +WMQ== X-Gm-Message-State: APjAAAUAsJ1+NkopRFU52eQzSHKuDbhfg9i5fMdT/oQFdcq/r31u8/mn DDyR6xgH6RS8rBcMrRQB0Z8= X-Google-Smtp-Source: APXvYqxCiNaVvdFuGx1EHIvyZ/qVW3RIpS2NmxW8P6HtapWUa9SJQAxcL2KD6HkTcQmn22Ao0CafaA== X-Received: by 2002:a5d:48cf:: with SMTP id p15mr29505wrs.46.1574410803823; Fri, 22 Nov 2019 00:20:03 -0800 (PST) Received: from localhost (prg-ext-pat.suse.com. [213.151.95.130]) by smtp.gmail.com with ESMTPSA id o189sm2740666wmo.23.2019.11.22.00.20.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 22 Nov 2019 00:20:03 -0800 (PST) Date: Fri, 22 Nov 2019 09:20:02 +0100 From: Michal Hocko To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: Roman Gushchin , "linux-mm@kvack.org" , Andrew Morton , Johannes Weiner , "linux-kernel@vger.kernel.org" , Kernel Team , "stable@vger.kernel.org" , Tejun Heo Subject: Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() Message-ID: <20191122082002.GP23213@dhcp22.suse.cz> References: <20191106225131.3543616-1-guro@fb.com> <20191113162934.GF19372@blackbody.suse.cz> <20191113170823.GA12464@castle.DHCP.thefacebook.com> <20191121152847.GA14375@blackbody.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191121152847.GA14375@blackbody.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 21-11-19 16:28:47, Michal Koutny wrote: > On Wed, Nov 13, 2019 at 05:08:29PM +0000, Roman Gushchin wrote: > > The thing here is that css_tryget_online() cannot pin the online state, > > so even if returned true, the cgroup can be offline at the return from > > the function. > Adding this for the record. > > The actual offlining happens only from css_killed_ref_fn, which is > percpu_ref_kill_and_confirm confirmation callback. That is only called > after RCU grace period. So, css_tryget_online will pin the online state > _inside_ rcu_read_{,un}lock section. Thanks for the confirmation. Maybe we should start with a trivial patch and document this first. We can go and cleanup bogus users on top. -- Michal Hocko SUSE Labs