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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 53B0AC352A2 for ; Thu, 6 Feb 2020 22:14:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2EC5B21927 for ; Thu, 6 Feb 2020 22:14:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727671AbgBFWOx (ORCPT ); Thu, 6 Feb 2020 17:14:53 -0500 Received: from mga02.intel.com ([134.134.136.20]:30453 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727450AbgBFWOx (ORCPT ); Thu, 6 Feb 2020 17:14:53 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Feb 2020 14:14:51 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,411,1574150400"; d="scan'208";a="404626475" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga005.jf.intel.com with ESMTP; 06 Feb 2020 14:14:49 -0800 Date: Fri, 7 Feb 2020 06:15:06 +0800 From: Wei Yang To: David Hildenbrand Cc: Baoquan He , Wei Yang , akpm@linux-foundation.org, osalvador@suse.de, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/sparsemem: pfn_to_page is not valid yet on SPARSEMEM Message-ID: <20200206221506.GA8863@richard> Reply-To: Wei Yang References: <20200206125343.9070-1-richardw.yang@linux.intel.com> <6d9e36cb-ee4a-00c8-447b-9b75a0262c3a@redhat.com> <20200206135016.GA25537@MiWiFi-R3L-srv> <87bb4563-481d-cce9-b916-50a098558210@redhat.com> <20200206140703.GB25537@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 06, 2020 at 03:37:40PM +0100, David Hildenbrand wrote: >On 06.02.20 15:07, Baoquan He wrote: >> On 02/06/20 at 02:55pm, David Hildenbrand wrote: >>> On 06.02.20 14:50, Baoquan He wrote: >>>> On 02/06/20 at 02:28pm, David Hildenbrand wrote: >>>>> On 06.02.20 13:53, Wei Yang wrote: >>>>>> When we use SPARSEMEM instead of SPARSEMEM_VMEMMAP, pfn_to_page() >>>>>> doesn't work before sparse_init_one_section() is called. This leads to a >>>>>> crash when hotplug memory. >>>>>> >>>>>> We should use memmap as it did. >>>>>> >>>>>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") >>>>>> Signed-off-by: Wei Yang >>>>>> CC: Dan Williams >>>>>> --- >>>>>> mm/sparse.c | 2 +- >>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/mm/sparse.c b/mm/sparse.c >>>>>> index 5a8599041a2a..2efb24ff8f96 100644 >>>>>> --- a/mm/sparse.c >>>>>> +++ b/mm/sparse.c >>>>>> @@ -882,7 +882,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn, >>>>>> * Poison uninitialized struct pages in order to catch invalid flags >>>>>> * combinations. >>>>>> */ >>>>>> - page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages); >>>>>> + page_init_poison(memmap, sizeof(struct page) * nr_pages); >>>>> >>>>> If you add sub-sections that don't fall onto the start of the section, >>>>> >>>>> pfn_to_page(start_pfn) != memmap >>>>> >>>>> and your patch would break that under SPARSEMEM_VMEMMAP if I am not wrong. >>>> >>>> It returns the pfn_to_page(pfn) from __populate_section_memmap() and >>>> assign to memmap in vmemmap case, how come it breaks anything. Correct >>>> me if I was wrong. >>> >>> I'm sorry, I can't follow :) Can you elaborate? >>> >>> Was your comment targeted at why the old code cannot be broken or why >>> this patch cannot be broken? >> >> Sorry for the confusion :-) the latter. I mean the returned memmap has been >> at the pfn_to_page(start_pfn) in SPARSEMEM_VMEMMAP case. > >Yeah, at least for SPARSEMEM_VMEMMAP it is indeed right. Thanks :) > > >Now, about SPARSEMEM: > >populate_section_memmap() does not care about nr_pages and will allocate >a memmap for the whole section. So, whenever we add sub-sections to a >section, we allocate a new memmap for the whole section. And we do >overwrite the memmap pointer in our section. ( sparse_add_section() ) > >That makes me assume that sub-section hot-add under SPARSEMEM is either > >a) never enabled and only works with SPARSEMEM_VMEMMAP >b) horribly broken > >And I think a) applies (looking at pfn_section_valid()). Therefore, we >don't have to care about sub-section hot-add specifics (and I would be >broken already) Yes, I am looking into this problem. Actually, there maybe another problem. Just get my brain refreshed, need some time to dig into. > >Acked-by: David Hildenbrand > >-- >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me