Re: [PATCH 3/5] mm/parisc: constify ptep_get() argument

On 7/24/26 17:48, Usama Arif wrote:
>=20
>=20
> On 24/07/2026 16:32, Pedro Falcato wrote:
>> On Fri, Jul 24, 2026 at 04:03:44PM +0100, Usama Arif wrote:
>>>
>>>
>>> On 24/07/2026 15:14, Matthew Wilcox wrote:
>>>> On Fri, Jul 24, 2026 at 02:36:59PM +0100, Usama Arif wrote:
>>>>>
>>>>>
>>>>> On 24/07/2026 11:20, Pedro Falcato wrote:
>>>>>> ptep_get() does not need write access to the PTE.
>>>>>>
>>>>>> Signed-off-by: Pedro Falcato <[email protected]>
>>>>>> ---
>>>>>>   arch/parisc/include/asm/pgtable.h | 2 +-
>>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>> hmm I think you might break build bisectibility if
>>>>> you separate out the patches, you should squash patch 3 and 4,
>>>>> with patch 1.
>>>>
>>>> I don't see how this breaks bisectability.  Can you elaborate on what
>>>> you think would break?
>>>
>>> Patch 1 does:
>>>
>>> -static inline pte_t ptep_get_lockless(pte_t *ptep)
>>> +static inline pte_t ptep_get_lockless(const pte_t *ptep)
>>>   {
>>>   	return ptep_get(ptep);
>>>   }
>>>
>>>
>>> ptep_get() takes a non-const arg till patch 3 for example for parsic.
>>> I don't think you can pass a const variable to non const function arg?
>>>
>>> So parsic won't compile in patch 1 and 2, powerprc wont compile
>>> for patches 1, 2 and 3..
>>
>> Aha, yes, nice catch! I'll have to rethink that. Maybe squashing the pa=
tches
>> would be the cleanest way forward.
>>
>=20
> Yes, squashing is the simplest way forward.
>=20
>> FWIW, the vast majority of architectures aren't doing funny things on
>> ptep_get(). E.g PA-RISC, loongarch only define these so they can use it=
 in
>> their own asm/pgtable.h. I'd really like to delete these but I can't te=
ll
>> if they are *actually* required.
>>
>=20
> Ah maybe there is something in git history on why it was needed?
>=20
> If not, hopefully someone from the arch lists could clarify..
I tried to remove ptep_get() and ptep_test_and_clear_young() from
arch/parisc/include/asm/pgtable.h, but this then triggers compile errors:

  CC      arch/parisc/kernel/asm-offsets.s
In file included from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/=
linux/mm.h:31,
                  from /home/cvs/parisc/git-kernel/linus-linux-2.6/include=
/linux/pid_namespace.h:7,
                  from /home/cvs/parisc/git-kernel/linus-linux-2.6/include=
/linux/ptrace.h:10,
                  from /home/cvs/parisc/git-kernel/linus-linux-2.6/arch/pa=
risc/kernel/asm-offsets.c:21:
/home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/pgtable.h: In fu=
nction =E2=80=98clear_young_dirty_ptes=E2=80=99:
/home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/pgtable.h:683:25=
: error: implicit declaration of function =E2=80=98ptep_test_and_clear_you=
ng=E2=80=99; did you mean =E2=80=98pmdp_test_and_clear_young=E2=80=99? [-W=
implicit-function-declaration]
   683 |                         ptep_test_and_clear_young(vma, addr, ptep=
);
       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~
       |                         pmdp_test_and_clear_young

So, I think the answer is, that the local copy of ptep_get() is used in th=
e parisc implementation of
ptep_test_and_clear_young() function.

Switching to the default include/linux/pgtable.h seems not easy doable....

Helge