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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 C9900C4360C for ; Thu, 10 Oct 2019 18:59:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9D19A206A1 for ; Thu, 10 Oct 2019 18:59:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727001AbfJJS7k (ORCPT ); Thu, 10 Oct 2019 14:59:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52758 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726424AbfJJS7k (ORCPT ); Thu, 10 Oct 2019 14:59:40 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 44CFF18C8902; Thu, 10 Oct 2019 18:59:39 +0000 (UTC) Received: from [10.36.116.80] (ovpn-116-80.ams2.redhat.com [10.36.116.80]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2A79E1001B09; Thu, 10 Oct 2019 18:59:35 +0000 (UTC) Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() To: Michal Hocko , Qian Cai Cc: Petr Mladek , Christian Borntraeger , Heiko Carstens , sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org, john.ogness@linutronix.de, akpm@linux-foundation.org, Vasily Gorbik , Peter Oberparleiter , linux-kernel@vger.kernel.org References: <20191009162339.GI6681@dhcp22.suse.cz> <6AAB77B5-092B-43E3-9F4B-0385DE1890D9@lca.pw> <20191010105927.GG18412@dhcp22.suse.cz> <1570713112.5937.26.camel@lca.pw> <20191010141820.GI18412@dhcp22.suse.cz> <1570718858.5937.28.camel@lca.pw> <20191010173040.GK18412@dhcp22.suse.cz> <1570729686.5937.30.camel@lca.pw> <20191010180626.GL18412@dhcp22.suse.cz> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <31b7049d-ba43-10a0-8434-18c9769ac0a5@redhat.com> Date: Thu, 10 Oct 2019 20:59:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <20191010180626.GL18412@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Thu, 10 Oct 2019 18:59:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10.10.19 20:06, Michal Hocko wrote: > On Thu 10-10-19 13:48:06, Qian Cai wrote: >> On Thu, 2019-10-10 at 19:30 +0200, Michal Hocko wrote: >>> On Thu 10-10-19 10:47:38, Qian Cai wrote: >>>> On Thu, 2019-10-10 at 16:18 +0200, Michal Hocko wrote: >>>>> On Thu 10-10-19 09:11:52, Qian Cai wrote: >>>>>> On Thu, 2019-10-10 at 12:59 +0200, Michal Hocko wrote: >>>>>>> On Thu 10-10-19 05:01:44, Qian Cai wrote: >>>>>>>> >>>>>>>> >>>>>>>>> On Oct 9, 2019, at 12:23 PM, Michal Hocko wrote: >>>>>>>>> >>>>>>>>> If this was only about the memory offline code then I would agree. But >>>>>>>>> we are talking about any printk from the zone->lock context and that is >>>>>>>>> a bigger deal. Besides that it is quite natural that the printk code >>>>>>>>> should be more universal and allow to be also called from the MM >>>>>>>>> contexts as much as possible. If there is any really strong reason this >>>>>>>>> is not possible then it should be documented at least. >>>>>>>> >>>>>>>> Where is the best place to document this? I am thinking about under >>>>>>>> the “struct zone” definition’s lock field in mmzone.h. >>>>>>> >>>>>>> I am not sure TBH and I do not think we have reached the state where >>>>>>> this would be the only way forward. >>>>>> >>>>>> How about I revised the changelog to focus on memory offline rather than making >>>>>> a rule that nobody should call printk() with zone->lock held? >>>>> >>>>> If you are to remove the CONFIG_DEBUG_VM printk then I am all for it. I >>>>> am still not convinced that fiddling with dump_page in the isolation >>>>> code is justified though. >>>> >>>> No, dump_page() there has to be fixed together for memory offline to be useful. >>>> What's the other options it has here? >>> >>> I would really prefer to not repeat myself >>> http://lkml.kernel.org/r/20191010074049.GD18412@dhcp22.suse.cz >> >> Care to elaborate what does that mean? I am confused on if you finally agree on >> no printk() while held zone->lock or not. You said "If there is absolutely >> no way around that then we might have to bite a bullet and consider some >> of MM locks a land of no printk." which makes me think you agreed, but your >> stance from the last reply seems you were opposite to it. > > I really do mean that the first step is to remove the dependency from > the printk and remove any allocation from the console callbacks. If that > turns out to be infeasible then we have to bite the bullet and think of > a way to drop all printks from all locks that participate in an atomic > allocation requests. > I second that and dropping the useless printk() as Michal mentioned. I would beg to not uglify the offlining/isolation code with __nolock variants or dropping locks somewhere down in a function. If everything fails, I rather want to see the prinkt's gone or returning details in a struct back to the caller, that can print it instead. e.g., struct unmovable_page_info { const char *reason; struct page *page; ... }; You should get the idea. -- Thanks, David / dhildenb