From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f71.google.com (mail-pa0-f71.google.com [209.85.220.71]) by kanga.kvack.org (Postfix) with ESMTP id AF8656B0005 for ; Fri, 20 May 2016 13:00:10 -0400 (EDT) Received: by mail-pa0-f71.google.com with SMTP id ke5so167440546pad.1 for ; Fri, 20 May 2016 10:00:10 -0700 (PDT) Received: from mail-pf0-x232.google.com (mail-pf0-x232.google.com. [2607:f8b0:400e:c00::232]) by mx.google.com with ESMTPS id uw13si28957289pab.200.2016.05.20.10.00.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 May 2016 10:00:08 -0700 (PDT) Received: by mail-pf0-x232.google.com with SMTP id 206so43281019pfu.0 for ; Fri, 20 May 2016 10:00:08 -0700 (PDT) Subject: Re: [PATCH] mm: page_is_guard return false when page_ext arrays are not allocated yet References: <1463610225-29060-1-git-send-email-yang.shi@linaro.org> <20160519002809.GA10245@js1304-P5Q-DELUXE> <4cb2025a-1b62-9c66-3d61-b457c92a7401@linaro.org> From: "Shi, Yang" Message-ID: Date: Fri, 20 May 2016 10:00:06 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Joonsoo Kim , Andrew Morton , Vlastimil Babka , LKML , Linux Memory Management List , linaro-kernel@lists.linaro.org On 5/19/2016 7:40 PM, Joonsoo Kim wrote: > 2016-05-20 2:18 GMT+09:00 Shi, Yang : >> On 5/18/2016 5:28 PM, Joonsoo Kim wrote: >>> >>> Vlastiml, thanks for ccing me on original bug report. >>> >>> On Wed, May 18, 2016 at 03:23:45PM -0700, Yang Shi wrote: >>>> >>>> When enabling the below kernel configs: >>>> >>>> CONFIG_DEFERRED_STRUCT_PAGE_INIT >>>> CONFIG_DEBUG_PAGEALLOC >>>> CONFIG_PAGE_EXTENSION >>>> CONFIG_DEBUG_VM >>>> >>>> kernel bootup may fail due to the following oops: >>>> >>>> BUG: unable to handle kernel NULL pointer dereference at (null) >>>> IP: [] free_pcppages_bulk+0x2d2/0x8d0 >>>> PGD 0 >>>> Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC >>>> Modules linked in: >>>> CPU: 11 PID: 106 Comm: pgdatinit1 Not tainted 4.6.0-rc5-next-20160427 #26 >>>> Hardware name: Intel Corporation S5520HC/S5520HC, BIOS >>>> S5500.86B.01.10.0025.030220091519 03/02/2009 >>>> task: ffff88017c080040 ti: ffff88017c084000 task.ti: ffff88017c084000 >>>> RIP: 0010:[] [] >>>> free_pcppages_bulk+0x2d2/0x8d0 >>>> RSP: 0000:ffff88017c087c48 EFLAGS: 00010046 >>>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001 >>>> RDX: 0000000000000980 RSI: 0000000000000080 RDI: 0000000000660401 >>>> RBP: ffff88017c087cd0 R08: 0000000000000401 R09: 0000000000000009 >>>> R10: ffff88017c080040 R11: 000000000000000a R12: 0000000000000400 >>>> R13: ffffea0019810000 R14: ffffea0019810040 R15: ffff88066cfe6080 >>>> FS: 0000000000000000(0000) GS:ffff88066cd40000(0000) >>>> knlGS:0000000000000000 >>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>> CR2: 0000000000000000 CR3: 0000000002406000 CR4: 00000000000006e0 >>>> Stack: >>>> ffff88066cd5bbd8 ffff88066cfe6640 0000000000000000 0000000000000000 >>>> 0000001f0000001f ffff88066cd5bbe8 ffffea0019810000 000000008118f53e >>>> 0000000000000009 0000000000000401 ffffffff0000000a 0000000000000001 >>>> Call Trace: >>>> [] free_hot_cold_page+0x192/0x1d0 >>>> [] __free_pages+0x5c/0x90 >>>> [] __free_pages_boot_core+0x11a/0x14e >>>> [] deferred_free_range+0x50/0x62 >>>> [] deferred_init_memmap+0x220/0x3c3 >>>> [] ? setup_per_cpu_pageset+0x35/0x35 >>>> [] kthread+0xf8/0x110 >>>> [] ret_from_fork+0x22/0x40 >>>> [] ? kthread_create_on_node+0x200/0x200 >>>> Code: 49 89 d4 48 c1 e0 06 49 01 c5 e9 de fe ff ff 4c 89 f7 44 89 4d b8 >>>> 4c 89 45 c0 44 89 5d c8 48 89 4d d0 e8 62 c7 07 00 48 8b 4d d0 <48> 8b 00 44 >>>> 8b 5d c8 4c 8b 45 c0 44 8b 4d b8 a8 02 0f 84 05 ff >>>> RIP [] free_pcppages_bulk+0x2d2/0x8d0 >>>> RSP >>>> CR2: 0000000000000000 >>>> >>>> The problem is lookup_page_ext() returns NULL then page_is_guard() tried >>>> to >>>> access it in page freeing. >>>> >>>> page_is_guard() depends on PAGE_EXT_DEBUG_GUARD bit of page extension >>>> flag, but >>>> freeing page might reach here before the page_ext arrays are allocated >>>> when >>>> feeding a range of pages to the allocator for the first time during >>>> bootup or >>>> memory hotplug. >>> >>> >>> Patch itself looks find to me because I also found that this kind of >>> problem happens during memory hotplug. So, we need to fix more sites, >>> all callers of lookup_page_ext(). >> >> >> Yes, I agree. I will come up with a patch or a couple of patches to check >> the return value of lookup_page_ext(). >> >>> >>> But, I'd like to know how your problem occurs during bootup. >>> debug_guardpage_enabled() is turned to 'enable' after page_ext is >>> initialized. Before that, page_is_guard() unconditionally returns >>> false so I think that the problem what you mentioned can't happen. >>> >>> Could you check that when debug_guardpage_enabled() returns 'enable' >>> and init_section_page_ext() is called? >> >> >> I think the problem is I have CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled, >> which will defer some struct pages initialization to "pgdatinitX" kernel >> thread in page_alloc_init_late(). But, page_ext_init() is called before it. >> So, it leads debug_guardpage_enabled() return true, but page extension is >> not allocated yet for the struct pages initialized by "pgdatinitX". > > No. After page_ext_init(), it is ensured that all page extension is initialized. > >> It sounds page_ext_init() should be called after page_alloc_init_late(). Or >> it should be just incompatible with CONFIG_DEFERRED_STRUCT_PAGE_INIT. >> >> I will try to move the init call around. > > We need to investigate more. I guess that problem is introduced by > CONFIG_DEFERRED_STRUCT_PAGE_INIT. It makes pfn_to_nid() invalid > until page_alloc_init_late() is done. That is a big side-effect. If > there is pfn walker > and it uses pfn_to_nid() between memmap_init_zone() and page_alloc_init_late(), > it also has same problem. So, we need to think how to fix it more > carefully. Thanks for the analysis. I think you are correct. Since pfn_to_nid() depends on memmap which has not been fully setup yet until page_alloc_init_late() is done. So, for such usecase early_pfn_to_nid() should be used. > > Anyway, to make sure that my assumption is true, could you confirm that > below change fix your problem? Yes, it does. > > Thanks. > > ----->8---------- > diff --git a/mm/page_ext.c b/mm/page_ext.c > index 2d864e6..cac5dc9 100644 > --- a/mm/page_ext.c > +++ b/mm/page_ext.c > @@ -391,7 +391,7 @@ void __init page_ext_init(void) > * -------------pfn--------------> > * N0 | N1 | N2 | N0 | N1 | N2|.... > */ > - if (pfn_to_nid(pfn) != nid) > + if (!early_pfn_in_nid(pfn nid)) early_pfn_in_nid() is static function in page_alloc.c. I'm supposed early_pfn_to_nid() should be used. Thanks, Yang > continue; > if (init_section_page_ext(pfn, nid)) > goto oom; > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . 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