1 files changed, 39 insertions, 9 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ac843d32b019..6d7296dd11b8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1510,16 +1510,29 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
 
 /*
  * Dissolve a given free hugepage into free buddy pages. This function does
- * nothing for in-use (including surplus) hugepages. Returns -EBUSY if the
- * dissolution fails because a give page is not a free hugepage, or because
- * free hugepages are fully reserved.
+ * nothing for in-use hugepages and non-hugepages.
+ * This function returns values like below:
+ *
+ *  -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
+ *          (allocated or reserved.)
+ *       0: successfully dissolved free hugepages or the page is not a
+ *          hugepage (considered as already dissolved)
  */
 int dissolve_free_huge_page(struct page *page)
 {
 	int rc = -EBUSY;
 
+	/* Not to disrupt normal path by vainly holding hugetlb_lock */
+	if (!PageHuge(page))
+		return 0;
+
 	spin_lock(&hugetlb_lock);
-	if (PageHuge(page) && !page_count(page)) {
+	if (!PageHuge(page)) {
+		rc = 0;
+		goto out;
+	}
+
+	if (!page_count(page)) {
 		struct page *head = compound_head(page);
 		struct hstate *h = page_hstate(head);
 		int nid = page_to_nid(head);
@@ -1564,11 +1577,9 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
 
 	for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
 		page = pfn_to_page(pfn);
-		if (PageHuge(page) && !page_count(page)) {
-			rc = dissolve_free_huge_page(page);
-			if (rc)
-				break;
-		}
+		rc = dissolve_free_huge_page(page);
+		if (rc)
+			break;
 	}
 
 	return rc;
@@ -3845,6 +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;
 		}