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 14:14:24 +0530

On 04/07/2016 02:46 PM, kbuild test robot wrote:
> Hi Anshuman,
> 
> [auto build test ERROR on powerpc/next]
> [also build test ERROR on v4.6-rc2 next-20160407]
> [if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Anshuman-Khandual/Enable-HugeTLB-page-migration-on-POWER/20160407-165841
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
> config: sparc64-allyesconfig (attached as .config)
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=sparc64 
> 
> All error/warnings (new ones prefixed by >>):
> 
>    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);
>       ^

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

diff --git a/arch/sparc/include/asm/pgtable_64.h
b/arch/sparc/include/asm/pgtable_64.h
index f089cfa..7b7e6a0 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -804,6 +804,7 @@ static inline unsigned long __pmd_page(pmd_t pmd)
 #define pmd_clear(pmdp)                        (pmd_val(*(pmdp)) = 0UL)
 #define pud_present(pud)               (pud_val(pud) != 0U)
 #define pud_clear(pudp)                        (pud_val(*(pudp)) = 0UL)
+#define pgd_page(pgd)                  (pgd_val(pgd))
 #define pgd_page_vaddr(pgd)            \
        ((unsigned long) __va(pgd_val(pgd)))
 #define pgd_present(pgd)               (pgd_val(pgd) != 0U)