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 BA686C10F14 for ; Thu, 10 Oct 2019 17:30:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9AF4B20659 for ; Thu, 10 Oct 2019 17:30:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570728647; bh=OADWXb31pxpne9eU4N/eWDE2zYL52xoyympOs/9bU8c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=X3FUjOyRKPgDPxvHUimzsNhiFiC6hB8QP7N8ODltotPsxq5zGsgqHsm6lfBp5JyHl XH5ng2Kmvt0gteY7NmRHpZL3wwgQwcaGICh+cri/8GB6GND1Q5eyo8GEDLj4kRD0+I zBTVwJUAA6Y/5EKeuwr0GbB5z1PXe9siLtjum5WM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726859AbfJJRaq (ORCPT ); Thu, 10 Oct 2019 13:30:46 -0400 Received: from mx2.suse.de ([195.135.220.15]:54486 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725862AbfJJRaq (ORCPT ); Thu, 10 Oct 2019 13:30:46 -0400 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 Content-Transfer-Encoding: 8bit In-Reply-To: <1570718858.5937.28.camel@lca.pw> 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 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 > By not holding zone->lock in dump_page() > from set_migratetype_isolate(), it even has a good side-effect to increase the > system throughput as dump_page() could be time-consuming. It may make the code a > bit cleaner by introducing a has_unmovable_pages_locked() version. I do not see why we should really optimize this cold path. -- Michal Hocko SUSE Labs