[PATCH 06/14] mm: handle_pte_fault() use pte_offset_map_maywrite_nolock()

[David Hildenbrand]

On 22.08.24 14:17, Qi Zheng wrote:
> Hi David,
> 
> On 2024/8/22 17:29, David Hildenbrand wrote:
>> On 21.08.24 12:03, Qi Zheng wrote:
>>>
>>>
> 
> [...]
> 
>>>>>>>>> -        vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm,
>>>>>>>>> vmf->pmd,
>>>>>>>>> -                         vmf->address, &vmf->ptl);
>>>>>>>>> +        vmf->pte = pte_offset_map_maywrite_nolock(vmf->vma->vm_mm,
>>>>>>>>> +                              vmf->pmd, vmf->address,
>>>>>>>>> +                              NULL, &vmf->ptl);
>>>>>>
>>>>>> I think we discussed that passing NULL should be forbidden for that
>>>>>> function.
>>>>>
>>>>> Yes, but for some maywrite case, there is no need to get pmdval to
>>>>> do pmd_same() check. So I passed NULL and added a comment to
>>>>> explain this.
>>>>
>>>> I wonder if it's better to pass a dummy variable instead. One has to
>>>> think harder why that is required compared to blindly passing "NULL" :)
>>>
>>> You are afraid that subsequent caller will abuse this function, right?
>>
>> Yes! "oh, I don't need a pmdval, why would I? let's just pass NULL,
>> easy" :)
>>
>>> My initial concern was that this would add a useless local vaiable, but
>>> perhaps that is not a big deal.
>>
>> How many of these "special" instances do we have?
> 
> We have 5 such special instances.
> 
>>
>>>
>>> Both are fine for me. ;)
>>
>> Also no strong opinion, but having to pass a variable makes you think
>> what you are supposed to do with it and why it is not optional.
> 
> Yeah, I added 'BUG_ON(!pmdvalp);' in pte_offset_map_ro_nolock(), and
> have updated the v2 version [1].

No BUG_ON please :) VM_WARN_ON_ONCE() is good enough.

-- 
Cheers,

David / dhildenb