Subject: Re: [PATCH 03/10] mm/hugetlb: Protect follow_huge_(pud|pgd) functions from race

From: Anshuman Khandual <[email-masked]>
Date: Mon, 18 Apr 2016 14:12:17 +0530

On 04/11/2016 11:34 AM, Anshuman Khandual wrote:
> On 04/07/2016 03:04 PM, kbuild test robot wrote:
>> > All errors (new ones prefixed by >>):
>> > 
>> >    mm/hugetlb.c: In function 'follow_huge_pud':
>>>>>> >>> >> mm/hugetlb.c:4360:3: error: implicit declaration of function 'pud_page' [-Werror=implicit-function-declaration]
>> >       page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
>> >       ^
>> >    mm/hugetlb.c:4360:8: warning: assignment makes pointer from integer without a cast
>> >       page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
>> >            ^
>> >    mm/hugetlb.c: In function 'follow_huge_pgd':
>> >    mm/hugetlb.c:4395:3: error: implicit declaration of function 'pgd_page' [-Werror=implicit-function-declaration]
>> >       page = pgd_page(*pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);
> Both the build errors here are because of the fact that pgd_page() is
> not available for some platforms and config options. It got missed as
> I ran only powerpc config options for build test purpose. My bad, will
> fix it.

The following change seems to fix the build problem on S390 but will
require some inputs from S390 maintainers regarding the functional
correctness of the patch.

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 2f66645..834a8a6 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -963,6 +963,8 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
 #define pte_page(x) pfn_to_page(pte_pfn(x))
 
 #define pmd_page(pmd) pfn_to_page(pmd_pfn(pmd))
+#define pud_page(pud) pud_val(pud)
+#define pgd_page(pgd) pgd_val(pgd)