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=-2.5 required=3.0 tests=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 81C3EC4360C for ; Thu, 10 Oct 2019 17:30:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 46D1720659 for ; Thu, 10 Oct 2019 17:30:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46D1720659 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C2CD98E0006; Thu, 10 Oct 2019 13:30:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BB7978E0003; Thu, 10 Oct 2019 13:30:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AA4E28E0006; Thu, 10 Oct 2019 13:30:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0103.hostedemail.com [216.40.44.103]) by kanga.kvack.org (Postfix) with ESMTP id 8287D8E0003 for ; Thu, 10 Oct 2019 13:30:46 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 1CA97181AC9AE for ; Thu, 10 Oct 2019 17:30:46 +0000 (UTC) X-FDA: 76028564892.07.shoe74_5df6bd5a3902a X-HE-Tag: shoe74_5df6bd5a3902a X-Filterd-Recvd-Size: 3619 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Thu, 10 Oct 2019 17:30:45 +0000 (UTC) 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 C4233AD9C; Thu, 10 Oct 2019 17:30:43 +0000 (UTC) Date: Thu, 10 Oct 2019 19:30:40 +0200 From: Michal Hocko To: 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 , david@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() Message-ID: <20191010173040.GK18412@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1570718858.5937.28.camel@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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: > > > > >=20 > > > > >=20 > > > > > > On Oct 9, 2019, at 12:23 PM, Michal Hocko = wrote: > > > > > >=20 > > > > > > If this was only about the memory offline code then I would a= gree. But > > > > > > we are talking about any printk from the zone->lock context a= nd that is > > > > > > a bigger deal. Besides that it is quite natural that the prin= tk 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 r= eason this > > > > > > is not possible then it should be documented at least. > > > > >=20 > > > > > Where is the best place to document this? I am thinking about u= nder > > > > > the =E2=80=9Cstruct zone=E2=80=9D definition=E2=80=99s lock fie= ld in mmzone.h. > > > >=20 > > > > I am not sure TBH and I do not think we have reached the state wh= ere > > > > this would be the only way forward. > > >=20 > > > 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? > >=20 > > 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. >=20 > 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 > By not holding zone->lock in dump_page() > from set_migratetype_isolate(), it even has a good side-effect to incre= ase the > system throughput as dump_page() could be time-consuming. It may make t= he code a > bit cleaner by introducing a has_unmovable_pages_locked() version. I do not see why we should really optimize this cold path. --=20 Michal Hocko SUSE Labs