[PATCH V13] mm/debug: Add tests validating architecture page table helpers

[Christophe Leroy]

Le 10/02/2020 à 06:35, Anshuman Khandual a écrit :
> 
> 
> On 02/10/2020 10:22 AM, Andrew Morton wrote:
>> On Thu, 6 Feb 2020 13:49:35 +0530 Anshuman Khandual <anshuman.khandual at arm.com> wrote:
>>
>>>
>>> On 02/06/2020 04:40 AM, kbuild test robot wrote:
>>>> Hi Anshuman,
>>>>
>>>> Thank you for the patch! Yet something to improve:
>>>>
>>>> [auto build test ERROR on powerpc/next]
>>>> [also build test ERROR on s390/features linus/master arc/for-next v5.5]
>>>> [cannot apply to mmotm/master tip/x86/core arm64/for-next/core next-20200205]
>>>> [if your patch is applied to the wrong git tree, please drop us a note to help
>>>> improve the system. BTW, we also suggest to use '--base' option to specify the
>>>> base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
>>>>
>>>> url:    https://github.com/0day-ci/linux/commits/Anshuman-Khandual/mm-debug-Add-tests-validating-architecture-page-table-helpers/20200205-215507
>>>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
>>>> config: ia64-allmodconfig (attached as .config)
>>>> compiler: ia64-linux-gcc (GCC) 7.5.0
>>>> reproduce:
>>>>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>>>>          chmod +x ~/bin/make.cross
>>>>          # save the attached .config to linux build tree
>>>>          GCC_VERSION=7.5.0 make.cross ARCH=ia64
>>>>
>>>> If you fix the issue, kindly add following tag
>>>> Reported-by: kbuild test robot <lkp at intel.com>
>>>>
>>>> All error/warnings (new ones prefixed by >>):
>>>>
>>>>     In file included from include/asm-generic/pgtable-nopud.h:8:0,
>>>>                      from arch/ia64/include/asm/pgtable.h:586,
>>>>                      from include/linux/mm.h:99,
>>>>                      from include/linux/highmem.h:8,
>>>>                      from mm/debug_vm_pgtable.c:14:
>>>>     mm/debug_vm_pgtable.c: In function 'pud_clear_tests':
>>>>>> include/asm-generic/pgtable-nop4d-hack.h:47:32: error: implicit declaration of function '__pgd'; did you mean '__p4d'? [-Werror=implicit-function-declaration]
>>>>      #define __pud(x)    ((pud_t) { __pgd(x) })
>>>>                                     ^
>>>>>> mm/debug_vm_pgtable.c:141:8: note: in expansion of macro '__pud'
>>>>       pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
>>>>             ^~~~~
>>>>>> include/asm-generic/pgtable-nop4d-hack.h:47:22: warning: missing braces around initializer [-Wmissing-braces]
>>>>      #define __pud(x)    ((pud_t) { __pgd(x) })
>>>>                           ^
>>>>>> mm/debug_vm_pgtable.c:141:8: note: in expansion of macro '__pud'
>>>>       pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
>>>>             ^~~~~
>>>>     cc1: some warnings being treated as errors
>>>
>>> This build failure is expected now given that we have allowed DEBUG_VM_PGTABLE
>>> with EXPERT without platform requiring ARCH_HAS_DEBUG_VM_PGTABLE. This problem
>>> i.e build failure caused without a platform __pgd(), is known to exist both on
>>> ia64 and arm (32bit) platforms. Please refer https://lkml.org/lkml/2019/9/24/314
>>> for details where this was discussed earlier.
>>>
>>
>> I'd prefer not to merge a patch which is known to cause build
>> regressions.  Is there some temporary thing we can do to prevent these
>> errors until arch maintainers(?) get around to implementing the
>> long-term fixes?
> 
> We could explicitly disable CONFIG_DEBUG_VM_PGTABLE on ia64 and arm platforms
> which will ensure that others can still use the EXPERT path.
> 
> config DEBUG_VM_PGTABLE
> 	bool "Debug arch page table for semantics compliance"
> 	depends on MMU
> 	depends on !(IA64 || ARM)
> 	depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
> 	default n if !ARCH_HAS_DEBUG_VM_PGTABLE
> 	default y if DEBUG_VM
> 

On both ia32 and arm, the fix is trivial.

Can we include the fix within this patch, just the same way as the 
mm_p4d_folded() fix for x86 ?

Christophe