On 2/1/21 2:40 PM, Peter Xu wrote:
> On Mon, Feb 01, 2021 at 02:11:55PM -0800, Axel Rasmussen wrote:
>> On Mon, Feb 1, 2021 at 11:21 AM Peter Xu <peterx@xxxxxxxxxx> wrote:
>>>
>>> On Thu, Jan 28, 2021 at 02:48:17PM -0800, Axel Rasmussen wrote:
>>>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>>>> index f94a35296618..79e1f0155afa 100644
>>>> --- a/include/linux/hugetlb.h
>>>> +++ b/include/linux/hugetlb.h
>>>> @@ -135,11 +135,14 @@ void hugetlb_show_meminfo(void);
>>>> unsigned long hugetlb_total_pages(void);
>>>> vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>>>> unsigned long address, unsigned int flags);
>>>> +#ifdef CONFIG_USERFAULTFD
>>>
>>> I'm confused why this is needed.. hugetlb_mcopy_atomic_pte() should only be
>>> called in userfaultfd.c, but if without uffd config set it won't compile
>>> either:
>>>
>>> obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
>>
>> With this series as-is, but *without* the #ifdef CONFIG_USERFAULTFD
>> here, we introduce a bunch of build warnings like this:
>>
>>
>>
>> In file included from ./include/linux/migrate.h:8:0,
>> from kernel/sched/sched.h:53,
>> from kernel/sched/isolation.c:10:
>> ./include/linux/hugetlb.h:143:12: warning: 'enum mcopy_atomic_mode'
>> declared inside parameter list
>> struct page **pagep);
>> ^
>> ./include/linux/hugetlb.h:143:12: warning: its scope is only this
>> definition or declaration, which is probably not what you want
>>
>> And similarly we get an error about the "mode" parameter having an
>> incomplete type in hugetlb.c.
>>
>>
>>
>> This is because enum mcopy_atomic_mode is defined in userfaultfd_k.h,
>> and that entire header is wrapped in a #ifdef CONFIG_USERFAULTFD. So
>> we either need to define enum mcopy_atomic_mode unconditionally, or we
>> need to #ifdef CONFIG_USERFAULTFD the references to it also.
>>
>> - I opted not to move it outside the #ifdef CONFIG_USERFAULTFD in
>> userfaultfd_k.h (defining it unconditionally), because that seemed
>> messy to me.
>> - I opted not to define it unconditionally in hugetlb.h, because we'd
>> have to move it to userfaultfd_k.h anyway when shmem or other users
>> are introduced. I'm planning to send a series to add this a few days
>> or so after this series is merged, so it seems churn-y to move it
>> then.
>> - It seemed optimal to not compile hugetlb_mcopy_atomic_pte anyway
>> (even ignoring adding the continue ioctl), since as you point out
>> userfaultfd is the only caller.
>>
>> Hopefully this clarifies this and the next two comments. Let me know
>> if you still feel strongly, I don't hate any of the alternatives, just
>> wanted to clarify that I had considered them and thought this approach
>> was best.
>
> Then I'd suggest you use a standalone patch to put hugetlb_mcopy_atomic_pte()
> into CONFIG_USERFAULTFD blocks, then propose your change with the minor mode.
> Note that there're two hugetlb_mcopy_atomic_pte() defined in hugetlb.h.
> Although I don't think it a problem since the other one is inlined - I think
> you should still put that one into the same ifdef:
>
> #ifdef CONFIG_USERFAULTFD
> static inline int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
> pte_t *dst_pte,
> struct vm_area_struct *dst_vma,
> unsigned long dst_addr,
> unsigned long src_addr,
> struct page **pagep)
> {
> BUG();
> return 0;
> }
> #endif /* CONFIG_USERFAULTFD */
>
> Let's also see whether Mike would have a preference on this.
>
No real preference. Just need to fix up the argument list in that
second definition.
--
Mike Kravetz
