mm/hugetlb.c: add NULL check of return value of huge_pte_offset

huge_pte_offset() could return NULL, so we need NULL check to avoid
potential NULL pointer dereferences.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7c02b9dadfb0..6cddfadaba03 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2690,7 +2690,8 @@ retry_avoidcopy:
                                 BUG_ON(huge_pte_none(pte));
                                 spin_lock(ptl);
                                 ptep = huge_pte_offset(mm, address & huge_page_mask(h));
-                                if (likely(pte_same(huge_ptep_get(ptep), pte)))
+                                if (likely(ptep &&
+                                           pte_same(huge_ptep_get(ptep), pte)))
                                         goto retry_avoidcopy;
                                 /*
                                  * race occurs while re-acquiring page table
@@ -2734,7 +2735,7 @@ retry_avoidcopy:
          */
         spin_lock(ptl);
         ptep = huge_pte_offset(mm, address & huge_page_mask(h));
-        if (likely(pte_same(huge_ptep_get(ptep), pte))) {
+        if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) {
                 ClearPagePrivate(new_page);
 
                 /* Break COW */