[PATCH v3 12/13] mm/debug_vm_pgtable/hugetlb: Disable hugetlb test on ppc64

[Aneesh Kumar K.V]

On 9/1/20 9:33 AM, Anshuman Khandual wrote:
> 
> 
> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
>> The seems to be missing quite a lot of details w.r.t allocating
>> the correct pgtable_t page (huge_pte_alloc()), holding the right
>> lock (huge_pte_lock()) etc. The vma used is also not a hugetlb VMA.
>>
>> ppc64 do have runtime checks within CONFIG_DEBUG_VM for most of these.
>> Hence disable the test on ppc64.
> 
> Would really like this to get resolved in an uniform and better way
> instead, i.e a modified hugetlb_advanced_tests() which works on all
> platforms including ppc64.
> 
> In absence of a modified version, I do realize the situation here,
> where DEBUG_VM_PGTABLE test either runs on ppc64 or just completely
> remove hugetlb_advanced_tests() from other platforms as well.
> 
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>> ---
>>   mm/debug_vm_pgtable.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index a188b6e4e37e..21329c7d672f 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -813,6 +813,7 @@ static void __init hugetlb_basic_tests(unsigned long pfn, pgprot_t prot)
>>   #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
>>   }
>>   
>> +#ifndef CONFIG_PPC_BOOK3S_64
>>   static void __init hugetlb_advanced_tests(struct mm_struct *mm,
>>   					  struct vm_area_struct *vma,
>>   					  pte_t *ptep, unsigned long pfn,
>> @@ -855,6 +856,7 @@ static void __init hugetlb_advanced_tests(struct mm_struct *mm,
>>   	pte = huge_ptep_get(ptep);
>>   	WARN_ON(!(huge_pte_write(pte) && huge_pte_dirty(pte)));
>>   }
>> +#endif
> 
> In the worst case if we could not get a new hugetlb_advanced_tests() test
> that works on all platforms, this might be the last fallback option. In
> which case, it will require a proper comment section with a "FIXME: ",
> explaining the current situation (and that #ifdef is temporary in nature)
> and a hugetlb_advanced_tests() stub when CONFIG_PPC_BOOK3S_64 is enabled.
> 
>>   #else  /* !CONFIG_HUGETLB_PAGE */
>>   static void __init hugetlb_basic_tests(unsigned long pfn, pgprot_t prot) { }
>>   static void __init hugetlb_advanced_tests(struct mm_struct *mm,
>> @@ -1065,7 +1067,9 @@ static int __init debug_vm_pgtable(void)
>>   	pud_populate_tests(mm, pudp, saved_pmdp);
>>   	spin_unlock(ptl);
>>   
>> +#ifndef CONFIG_PPC_BOOK3S_64
>>   	hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
>> +#endif
>

I actually wanted to add #ifdef BROKEN. That test is completely broken. 
Infact I would suggest to remove that test completely.



> #ifdef will not be required here as there would be a stub definition
> for hugetlb_advanced_tests() when CONFIG_PPC_BOOK3S_64 is enabled.
> 
>>   
>>   	spin_lock(&mm->page_table_lock);
>>   	p4d_clear_tests(mm, p4dp);
>>
> 
> But again, we should really try and avoid taking this path.
> 

To be frank i am kind of frustrated with how this patch series is being 
looked at. We pushed a completely broken test to upstream and right now 
we have a code in upstream that crash when booted on ppc64. My attempt 
has been to make progress here and you definitely seems to be not in 
agreement to that.

At this point I am tempted to suggest we remove the DEBUG_VM_PGTABLE 
support on ppc64 because AFAIU it doesn't add any value.


-aneesh