On Thu, Dec 24, 2015 at 3:51 AM, Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > This patch fixes regression caused by patch > "mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd" > > The patch makes pmd_trans_huge() check and "page = pmd_page(*pmd)" after > __split_huge_pmd_locked(). It can never succeed, since the pmd already > points to a page table. As result the page is never get munlocked. > > It causes crashes like this: > http://lkml.kernel.org/r/5661FBB6.6050307@xxxxxxxxxx > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > mm/huge_memory.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 99f2a0ecb621..1a988d9b86ef 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3024,14 +3024,12 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > ptl = pmd_lock(mm, pmd); > if (unlikely(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > goto out; > - __split_huge_pmd_locked(vma, pmd, haddr, false); > - > - if (pmd_trans_huge(*pmd)) > - page = pmd_page(*pmd); > - if (page && PageMlocked(page)) > + page = pmd_page(*pmd); > + if (PageMlocked(page)) > get_page(page); > else > page = NULL; > + __split_huge_pmd_locked(vma, pmd, haddr, false); Since dax pmd mappings may not have a backing struct page I think this additionally needs the following: 8<----- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 4eae97325e95..c4eccfa836f4 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3025,11 +3025,13 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, ptl = pmd_lock(mm, pmd); if (unlikely(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) goto out; - page = pmd_page(*pmd); - if (PageMlocked(page)) - get_page(page); - else - page = NULL; + else if (pmd_trans_huge(*pmd)) { + page = pmd_page(*pmd); + if (PageMlocked(page)) + get_page(page); + else + page = NULL; + } __split_huge_pmd_locked(vma, pmd, haddr, false); out: spin_unlock(ptl); -- 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>