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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 39359C433E1 for ; Mon, 3 Aug 2020 15:09:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 047E620775 for ; Mon, 3 Aug 2020 15:09:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 047E620775 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7F8018D0105; Mon, 3 Aug 2020 11:09:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7A9908D0081; Mon, 3 Aug 2020 11:09:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6BFD68D0105; Mon, 3 Aug 2020 11:09:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0197.hostedemail.com [216.40.44.197]) by kanga.kvack.org (Postfix) with ESMTP id 568438D0081 for ; Mon, 3 Aug 2020 11:09:01 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 12C881EF2 for ; Mon, 3 Aug 2020 15:09:01 +0000 (UTC) X-FDA: 77109590082.14.self76_1f065b326f9e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin14.hostedemail.com (Postfix) with ESMTP id E1BA3182299A7 for ; Mon, 3 Aug 2020 15:09:00 +0000 (UTC) X-HE-Tag: self76_1f065b326f9e X-Filterd-Recvd-Size: 2205 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Mon, 3 Aug 2020 15:09:00 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 87089AF76; Mon, 3 Aug 2020 15:09:14 +0000 (UTC) Date: Mon, 3 Aug 2020 17:08:58 +0200 From: Michal Hocko To: Johannes Weiner Cc: Roman Gushchin , Andrew Morton , Christoph Lameter , Shakeel Butt , linux-mm@kvack.org, Vlastimil Babka , kernel-team@fb.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 05/19] mm: memcontrol: decouple reference counting from page accounting Message-ID: <20200803150858.GW5174@dhcp22.suse.cz> References: <20200623174037.3951353-1-guro@fb.com> <20200623174037.3951353-6-guro@fb.com> <20200803090033.GE5174@dhcp22.suse.cz> <20200803150349.GA502356@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200803150349.GA502356@cmpxchg.org> X-Rspamd-Queue-Id: E1BA3182299A7 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 03-08-20 11:03:49, Johannes Weiner wrote: > On Mon, Aug 03, 2020 at 11:00:33AM +0200, Michal Hocko wrote: > > On Tue 23-06-20 10:40:23, Roman Gushchin wrote: > > > @@ -5456,7 +5460,10 @@ static int mem_cgroup_move_account(struct page *page, > > > */ > > > smp_mb(); > > > > > > - page->mem_cgroup = to; /* caller should have done css_get */ > > > + css_get(&to->css); > > > + css_put(&from->css); > > > + > > > + page->mem_cgroup = to; > > > > > > __unlock_page_memcg(from); > > > > What prevents from memcg to be released here? > > ->attach_task() and kill_css() are exclusive through the cgroup_mutex, > so the base ref cannot disappear from under us during this operation. OK, is this worth a comment? Reference counting before other operation on the object always makes me worried and those details are hidden elsewhere. Btw. with the follow up fix from Hugh Acked-by: Michal Hocko -- Michal Hocko SUSE Labs