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_PASS,USER_AGENT_MUTT autolearn=ham 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 1649DC04AA7 for ; Mon, 13 May 2019 15:31:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D9F2B2084A for ; Mon, 13 May 2019 15:31:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557761509; bh=GggIqFls8VfMFS9pcpCN8hYqKymwsP/J0ay41YX7oBQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=k66K22oheVse2rZI7DnDJCEVLSEI+cYXeqWLfLvzeoQsXoprVBpwzduI2L4yASxmf +aTytKiyKwAe5VMTklzgMJF6uqvMeariSdjvjuHQ0Zl3i5O3OyOICbOm9O85o+b7/0 nCOvcNZ/yxvNLvIRb9qHoy4PHYJ1tlau/5P+I8kU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731370AbfEMPbt (ORCPT ); Mon, 13 May 2019 11:31:49 -0400 Received: from mx2.suse.de ([195.135.220.15]:47928 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728760AbfEMPbs (ORCPT ); Mon, 13 May 2019 11:31:48 -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 3DE8BAFCE; Mon, 13 May 2019 15:31:46 +0000 (UTC) Date: Mon, 13 May 2019 17:31:43 +0200 From: Michal Hocko To: Qian Cai Cc: akpm@linux-foundation.org, brho@google.com, kernelfans@gmail.com, dave.hansen@intel.com, rppt@linux.ibm.com, peterz@infradead.org, mpe@ellerman.id.au, mingo@elte.hu, osalvador@suse.de, luto@kernel.org, tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -next v2] mm/hotplug: fix a null-ptr-deref during NUMA boot Message-ID: <20190513153143.GK24036@dhcp22.suse.cz> References: <20190512054829.11899-1-cai@lca.pw> <20190513124112.GH24036@dhcp22.suse.cz> <1557755039.6132.23.camel@lca.pw> <20190513140448.GJ24036@dhcp22.suse.cz> <1557760846.6132.25.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1557760846.6132.25.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 Mon 13-05-19 11:20:46, Qian Cai wrote: > On Mon, 2019-05-13 at 16:04 +0200, Michal Hocko wrote: > > On Mon 13-05-19 09:43:59, Qian Cai wrote: > > > On Mon, 2019-05-13 at 14:41 +0200, Michal Hocko wrote: > > > > On Sun 12-05-19 01:48:29, Qian Cai wrote: > > > > > The linux-next commit ("x86, numa: always initialize all possible > > > > > nodes") introduced a crash below during boot for systems with a > > > > > memory-less node. This is due to CPUs that get onlined during SMP boot, > > > > > but that onlining triggers a page fault in bus_add_device() during > > > > > device registration: > > > > > > > > > > error = sysfs_create_link(&bus->p->devices_kset->kobj, > > > > > > > > > > bus->p is NULL. That "p" is the subsys_private struct, and it should > > > > > have been set in, > > > > > > > > > > postcore_initcall(register_node_type); > > > > > > > > > > but that happens in do_basic_setup() after smp_init(). > > > > > > > > > > The old code had set this node online via alloc_node_data(), so when it > > > > > came time to do_cpu_up() -> try_online_node(), the node was already up > > > > > and nothing happened. > > > > > > > > > > Now, it attempts to online the node, which registers the node with > > > > > sysfs, but that can't happen before the 'node' subsystem is registered. > > > > > > > > > > Since kernel_init() is running by a kernel thread that is in > > > > > SYSTEM_SCHEDULING state, fixed this by skipping registering with sysfs > > > > > during the early boot in __try_online_node(). > > > > > > > > Relying on SYSTEM_SCHEDULING looks really hackish. Why cannot we simply > > > > drop try_online_node from do_cpu_up? Your v2 remark below suggests that > > > > we need to call node_set_online because something later on depends on > > > > that. Btw. why do we even allocate a pgdat from this path? This looks > > > > really messy. > > > > > > See the commit cf23422b9d76 ("cpu/mem hotplug: enable CPUs online before > > > local > > > memory online") > > > > > > It looks like try_online_node() in do_cpu_up() is needed for memory hotplug > > > which is to put its node online if offlined and then hotadd_new_pgdat() > > > calls > > > build_all_zonelists() to initialize the zone list. > > > > Well, do we still have to followthe logic that the above (unreviewed) > > commit has established? The hotplug code in general made a lot of ad-hoc > > design decisions which had to be revisited over time. If we are not > > allocating pgdats for newly added memory then we should really make sure > > to do so at a proper time and hook. I am not sure about CPU vs. memory > > init ordering but even then I would really prefer if we could make the > > init less obscure and _documented_. > > I don't know, but I think it is a good idea to keep the existing logic rather > than do a big surgery Adding more hacks just doesn't make the situation any better. > unless someone is able to confirm it is not breaking NUMA > node physical hotplug. I have a machine to test whole node offline. I am just busy to prepare a patch myself. I can have it tested though. -- Michal Hocko SUSE Labs