Messages in this thread | | | Subject | Re: [PATCH v2 01/12] mm/debug_vm_pgtable: Introduce struct pgtable_debug_args | From | Gavin Shan <> | Date | Wed, 21 Jul 2021 09:29:43 +1000 |
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On 7/20/21 4:42 PM, Anshuman Khandual wrote: > On 7/19/21 6:31 PM, Gavin Shan wrote: >>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && >>> + has_transparent_hugepage()) { >>> + page = alloc_pages(GFP_KERNEL, HPAGE_PMD_ORDER); >>> + if (page) { >>> + args->pmd_pfn = page_to_pfn(page); >>> + args->pte_pfn = args->pmd_pfn; >>> + return 0; >>> + } >>> + } >>> + >> >> As syzbot reported against v1 series, we could allocate pages larger than (1 << (MAX_ORDER - 1)) here. >> So __GFP_NOWARN is needed here. I will fix it in v3 series. > > I could find the following build error reported from lkp on V2. > > mm/debug_vm_pgtable.c:445:8: warning: variable 'pud' set but not used [-Wunused-but-set-variable] >
Yes, The following line is missed in PATCH[v2 09/12] and fixed in PATCH[v3 09/12]: WARN_ON(!pud_none(pud)). With this line added, the variable @pud is used in v3.
> Could you please point to the syzbot reported problem on V1 as you > have mentioned above. Are there configs where HPAGE_[PMD|PUD]_ORDER > is greater than (MAX_ORDER - 1) ? If yes, how adding __GFP_NOWARN > solves the problem ? >
https://syzkaller.appspot.com/bug?extid=8730ec44a441a434a2c8 https://syzkaller.appspot.com/x/.config?x=29a82c885e192046
The kernel config has the following options:
CONFIG_X86_64=y CONFIG_TRANSPARENT_HUGEPAGE=y CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD=y #define PUD_SHIFT 30 #define PMD_SHIFT 21
CONFIG_FORCE_MAX_ZONEORDER=n #define MAX_ORDER 11
(HPAGE_PUD_SHIFT - PAGE_SHIFT) >= (1 << MAX_ORDER) (HPAGE_PMD_ORDER) < (1 << MAX_ORDER)
The warning is triggered in the following path, __GFP_NOWARN helps to avoid the WARNING_ON_ONCE(), but NULL is returned as expected.
alloc_pages __alloc_pages
if (unlikely(order >= MAX_ORDER)) { WARN_ON_ONCE(!(gfp & __GFP_NOWARN)); return NULL; }
Thanks, Gavin
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