linux-kernel - Re: [PATCH v2 01/12] mm/debug_vm_pgtable: Introduce struct pgtable_debug

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Date:   Tue, 20 Jul 2021 12:12:35 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will@...nel.org, akpm@...ux-foundation.org, chuhu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH v2 01/12] mm/debug_vm_pgtable: Introduce struct
 pgtable_debug_args



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]

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 ?