Messages in this thread | | | Subject | Re: [PATCH] mm: page_is_guard return false when page_ext arrays are not allocated yet | From | "Shi, Yang" <> | Date | Fri, 20 May 2016 10:00:06 -0700 |
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On 5/19/2016 7:40 PM, Joonsoo Kim wrote: > 2016-05-20 2:18 GMT+09:00 Shi, Yang <yang.shi@linaro.org>: >> 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: [<ffffffff8118d982>] 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:[<ffffffff8118d982>] [<ffffffff8118d982>] >>>> 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: >>>> [<ffffffff8118f602>] free_hot_cold_page+0x192/0x1d0 >>>> [<ffffffff8118f69c>] __free_pages+0x5c/0x90 >>>> [<ffffffff8262a676>] __free_pages_boot_core+0x11a/0x14e >>>> [<ffffffff8262a6fa>] deferred_free_range+0x50/0x62 >>>> [<ffffffff8262aa46>] deferred_init_memmap+0x220/0x3c3 >>>> [<ffffffff8262a826>] ? setup_per_cpu_pageset+0x35/0x35 >>>> [<ffffffff8108b1f8>] kthread+0xf8/0x110 >>>> [<ffffffff81c1b732>] ret_from_fork+0x22/0x40 >>>> [<ffffffff8108b100>] ? 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 [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0 >>>> RSP <ffff88017c087c48> >>>> 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; >
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