On Wed 22-11-17 15:19:21, Kirill A. Shutemov wrote:
I've made mistake during converting hugetlb code to 5-level paging: in huge_pte_alloc() we have to use p4d_alloc(), not p4d_offset(). Otherwise it leads to crash -- NULL-pointer dereference in pud_alloc() if p4d table is not yet allocated.
Ups, I have completely missed that when reviewing the patch. Sorry about that.
It only can happen in 5-level paging mode. In 4-level paging mode p4d_offset() always returns pgd, so we are fine.
Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging") Cc: stable@vger.kernel.org # v4.11+
Acked-by: Michal Hocko mhocko@suse.com
mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2d2ff5e8bf2b..94a4c0b63580 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4617,7 +4617,9 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, pte_t *pte = NULL; pgd = pgd_offset(mm, addr);
- p4d = p4d_offset(pgd, addr);
- p4d = p4d_alloc(mm, pgd, addr);
- if (!p4d)
return NULL;-- 2.15.0