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 50110C5DF60 for ; Fri, 8 Nov 2019 08:53:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 194BD21882 for ; Fri, 8 Nov 2019 08:53:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573203221; bh=i7PdomCShrkSx73U4mHHd12/2AVm7/eIE5IqfUFKkN4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=lUBzXZC7e50FYyOB/tZ8/37+eC8WTMkMfqZkriOgNFnu6on4toVU4iGvJDbFkcGo3 XxevnV5pH+tup2mfEitrFpRSwEyPzMMCVTm2b1bco0Q7REuqNgVD+WICas+Nb7odWU 0Yxg20vLEK9oo+16OcfFep+4nIj7bpNDvKkICB8E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728513AbfKHIxk (ORCPT ); Fri, 8 Nov 2019 03:53:40 -0500 Received: from mx2.suse.de ([195.135.220.15]:40428 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726072AbfKHIxk (ORCPT ); Fri, 8 Nov 2019 03:53:40 -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 BD938B219; Fri, 8 Nov 2019 08:53:38 +0000 (UTC) Date: Fri, 8 Nov 2019 09:53:37 +0100 From: Michal Hocko To: Roman Gushchin Cc: "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: <20191108085337.GA15658@dhcp22.suse.cz> References: <20191106225131.3543616-1-guro@fb.com> <20191107122125.GS8314@dhcp22.suse.cz> <20191107164236.GB2919@castle.dhcp.thefacebook.com> <20191107170200.GX8314@dhcp22.suse.cz> <20191107224107.GA8219@castle.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191107224107.GA8219@castle.DHCP.thefacebook.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 07-11-19 22:41:13, Roman Gushchin wrote: > On Thu, Nov 07, 2019 at 06:02:00PM +0100, Michal Hocko wrote: > > On Thu 07-11-19 16:42:41, Roman Gushchin wrote: [...] > > > It's an exiting task with the PF_EXITING flag set and it's in their late stages > > > of life. > > > > This is a signal delivery path AFAIU (get_signal) and the coredumping > > happens before do_exit. My understanding is that that unlinking > > happens from cgroup_exit. So either I am misreading the backtrace or > > there is some other way to leave cgroups or there is something more > > going on. > > Yeah, you're right. I have no better explanation for this and the similar, > mentioned in the commit bsd accounting issue, Tejun mentioned bsd accounting issue as well, but I do not see any explicit reference to it in neither of the two patches. > than some very rare race condition > that allows cgroups to be offlined with a task inside. > > I'll think more about it. Thanks a lot. As I've said, I am not opposing this change once we have a proper changelog but I find the explanation really weak. If there is a race then it should be fixed as well. Thanks! -- Michal Hocko SUSE Labs