On Thu, Jun 9, 2022 at 4:24 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote: > > On Mon, Jun 6, 2022 at 2:44 PM Yang Shi <shy828301@xxxxxxxxx> wrote: > > > > The hugepage_vma_check() already checked it, so remove the redundant > > check. > > > > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> > > --- > > mm/khugepaged.c | 3 --- > > 1 file changed, 3 deletions(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index d0f8020164fc..7a5d1c1a1833 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -966,9 +966,6 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > > return SCAN_ADDRESS_RANGE; > > if (!hugepage_vma_check(vma, vma->vm_flags)) > > return SCAN_VMA_CHECK; > > - /* Anon VMA expected */ > > - if (!vma->anon_vma || !vma_is_anonymous(vma)) > > - return SCAN_VMA_CHECK; > > return 0; > > } > > > > -- > > 2.26.3 > > > > > > So, I don't know if this is possible, but I wonder if there is a race here: > > hugepage_vma_revalidate() is called in the anon path when mmap_lock > after dropped + reacquired, and we want to refind / revalidate the > vma, since it might have changed. > > There is the possibility that the memory was unmapped, then remapped > as file or shmem. If so, hugepage_vma_check() could return true > without actually checking vma->anon_vma || !vma_is_anonymous(vma) - > and we probably do want to (re)validate that this is indeed still an > anon vma. Nice catch! Totally possible. I did overlook this. I will drop this patch in the next version or maybe making the comment clearer is a better choice.
