On Thu, Jun 16, 2016 at 02:47:14PM +0300, Ebru Akagunduz wrote: > On Wed, Jun 15, 2016 at 11:06:10PM +0300, Kirill A. Shutemov wrote: > > Vlastimil noted[1] that pmd can be no longer valid after we drop > > mmap_sem. We need recheck it once mmap_sem taken again. > > > > [1] http://lkml.kernel.org/r/12918dcd-a695-c6f4-e06f-69141c5f357f@xxxxxxx > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > --- > > mm/huge_memory.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index d7ccc8558187..0efdad975659 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2437,6 +2437,9 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > > /* vma is no longer available, don't continue to swapin */ > > if (hugepage_vma_revalidate(mm, address)) > > return false; > > + /* check if the pmd is still valid */ > > + if (mm_find_pmd(mm, address) != pmd) > > + return false; > > } > Thanks for fixing this. > > > if (ret & VM_FAULT_ERROR) { > > trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0); > > @@ -2522,6 +2525,9 @@ static void collapse_huge_page(struct mm_struct *mm, > > result = hugepage_vma_revalidate(mm, address); > > if (result) > > goto out; > > + /* check if the pmd is still valid */ > > + if (mm_find_pmd(mm, address) != pmd) > > + goto out; > > > However here, I don't know do we need to check pmd. > Because in collapse_huge_page; pmd is newly created, > after taking mmap_sem read: > { > > pmd_t *pmd, _pmd; > pte_t *pte; > ... > down_read(&mm->mmap_sem); > result = hugepage_vma_revalidate(mm, address); > ... > pmd = mm_find_pmd(mm, address); > ... > > Therefore it did not seem like a problem for me. I guess you're looking on the first hugepage_vma_revalidate() in collapse_huge_page(). The patch fixes issue after the second one: pmd_t *pmd, _pmd; pte_t *pte; ... down_read(&mm->mmap_sem); result = hugepage_vma_revalidate(mm, address); ... pmd = mm_find_pmd(mm, address); ... up_read(&mm->mmap_sem); ... down_write(&mm->mmap_sem); result = hugepage_vma_revalidate(mm, address); if (mm_find_pmd(mm, address) != pmd) goto out; -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>