Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
> On Tue, 7 May 2013 02:19:48 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
>
>> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>>
>> We should use pmdp_set_access_flags to update access flags. Archs like powerpc
>> use extra checks(_PAGE_BUSY) when updating a hugepage PTE. A set_pmd_at doesn't
>> do those checks. We should use set_pmd_at only when updating a none hugepage PTE.
>>
>> ...
>>
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1265,7 +1265,9 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
>> * young bit, instead of the current set_pmd_at.
>> */
>> _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
>> - set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
>> + if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
>> + pmd, _pmd, 1))
>> + update_mmu_cache_pmd(vma, addr, pmd);
>> }
>> if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
>> if (page->mapping && trylock_page(page)) {
>
> <canned message>
> When writing a changelog, please describe the end-user-visible effects
> of the bug, so that others can more easily decide which kernel
> version(s) should be fixed, and so that downstream kernel maintainers
> can more easily work out whether this patch will fix a problem which
> they or their customers are observing.
I found that reading code while debugging some crashes with THP on
ppc64. So user visible effects would mostly be some random crashes.
I will make sure to document the user visible effects next time.
-aneesh
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