1 files changed, 19 insertions, 0 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ede7e7f5d1ab..6d7296dd11b8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3856,6 +3856,25 @@ retry:
 
                 page = alloc_huge_page(vma, haddr, 0);
                 if (IS_ERR(page)) {
+                        /*
+                         * Returning error will result in faulting task being
+                         * sent SIGBUS.  The hugetlb fault mutex prevents two
+                         * tasks from racing to fault in the same page which
+                         * could result in false unable to allocate errors.
+                         * Page migration does not take the fault mutex, but
+                         * does a clear then write of pte's under page table
+                         * lock.  Page fault code could race with migration,
+                         * notice the clear pte and try to allocate a page
+                         * here.  Before returning error, get ptl and make
+                         * sure there really is no pte entry.
+                         */
+                        ptl = huge_pte_lock(h, mm, ptep);
+                        if (!huge_pte_none(huge_ptep_get(ptep))) {
+                                ret = 0;
+                                spin_unlock(ptl);
+                                goto out;
+                        }
+                        spin_unlock(ptl);
                         ret = vmf_error(PTR_ERR(page));
                         goto out;
                 }