From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f69.google.com (mail-pa0-f69.google.com [209.85.220.69]) by kanga.kvack.org (Postfix) with ESMTP id 508096B025F for ; Tue, 24 May 2016 12:37:24 -0400 (EDT) Received: by mail-pa0-f69.google.com with SMTP id x1so23643136pav.3 for ; Tue, 24 May 2016 09:37:24 -0700 (PDT) Received: from mail-pa0-x22f.google.com (mail-pa0-x22f.google.com. [2607:f8b0:400e:c03::22f]) by mx.google.com with ESMTPS id t5si5732917pac.75.2016.05.24.09.37.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 May 2016 09:37:23 -0700 (PDT) Received: by mail-pa0-x22f.google.com with SMTP id qo8so8278315pab.1 for ; Tue, 24 May 2016 09:37:22 -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>

<20160524053714.GB32186@js1304-P5Q-DELUXE> From: "Shi, Yang" Message-ID: Date: Tue, 24 May 2016 09:37:21 -0700 MIME-Version: 1.0 In-Reply-To: <20160524053714.GB32186@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Andrew Morton , Vlastimil Babka , LKML , Linux Memory Management List , linaro-kernel@lists.linaro.org On 5/23/2016 10:37 PM, Joonsoo Kim wrote: > On Fri, May 20, 2016 at 10:00:06AM -0700, Shi, Yang wrote: >> 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 for checking. Then, please revert your patch "mm: call > page_ext_init() after all struct pages are initialized" and apply this > change, because deferring page_ext_init() would make page owner which > uses page_ext miss some early page allocation callsites. Although it > already miss some early page allocation callsites, we don't need to > miss more. Definitely agree. I will come up with an incremental patch to adopt the new solution. Thanks, Yang > > Thanks. > -- 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/ . Don't email: email@kvack.org