1 files changed, 58 insertions, 9 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index e2b0afd0a031..4d5a681923bb 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -412,6 +412,29 @@ out:
 	up_read(&mm->mmap_sem);
 }
 
+static struct page *page_trans_compound_anon(struct page *page)
+{
+	if (PageTransCompound(page)) {
+		struct page *head;
+		head = compound_head(page);
+		/*
+		 * head may be a dangling pointer.
+		 * __split_huge_page_refcount clears PageTail
+		 * before overwriting first_page, so if
+		 * PageTail is still there it means the head
+		 * pointer isn't dangling.
+		 */
+		if (head != page) {
+			smp_rmb();
+			if (!PageTransCompound(page))
+				return NULL;
+		}
+		if (PageAnon(head))
+			return head;
+	}
+	return NULL;
+}
+
 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 {
 	struct mm_struct *mm = rmap_item->mm;
@@ -431,7 +454,7 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 	page = follow_page(vma, addr, FOLL_GET);
 	if (IS_ERR_OR_NULL(page))
 		goto out;
-	if (PageAnon(page) && !PageTransCompound(page)) {
+	if (PageAnon(page) || page_trans_compound_anon(page)) {
 		flush_anon_page(vma, page, addr);
 		flush_dcache_page(page);
 	} else {
@@ -709,6 +732,7 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 	if (addr == -EFAULT)
 		goto out;
 
+	BUG_ON(PageTransCompound(page));
 	ptep = page_check_address(page, mm, addr, &ptl, 0);
 	if (!ptep)
 		goto out;
@@ -784,6 +808,7 @@ static int replace_page(struct vm_area_struct *vma, struct page *page,
 		goto out;
 
 	pmd = pmd_offset(pud, addr);
+	BUG_ON(pmd_trans_huge(*pmd));
 	if (!pmd_present(*pmd))
 		goto out;
 
@@ -811,6 +836,33 @@ out:
 	return err;
 }
 
+static int page_trans_compound_anon_split(struct page *page)
+{
+	int ret = 0;
+	struct page *transhuge_head = page_trans_compound_anon(page);
+	if (transhuge_head) {
+		/* Get the reference on the head to split it. */
+		if (get_page_unless_zero(transhuge_head)) {
+			/*
+			 * Recheck we got the reference while the head
+			 * was still anonymous.
+			 */
+			if (PageAnon(transhuge_head))
+				ret = split_huge_page(transhuge_head);
+			else
+				/*
+				 * Retry later if split_huge_page run
+				 * from under us.
+				 */
+				ret = 1;
+			put_page(transhuge_head);
+		} else
+			/* Retry later if split_huge_page run from under us. */
+			ret = 1;
+	}
+	return ret;
+}
+
 /*
  * try_to_merge_one_page - take two pages and merge them into one
  * @vma: the vma that holds the pte pointing to page
@@ -831,6 +883,9 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
 
 	if (!(vma->vm_flags & VM_MERGEABLE))
 		goto out;
+	if (PageTransCompound(page) && page_trans_compound_anon_split(page))
+		goto out;
+	BUG_ON(PageTransCompound(page));
 	if (!PageAnon(page))
 		goto out;
 
@@ -1285,14 +1340,8 @@ next_mm:
 				cond_resched();
 				continue;
 			}
-			if (PageTransCompound(*page)) {
-				put_page(*page);
-				ksm_scan.address &= HPAGE_PMD_MASK;
-				ksm_scan.address += HPAGE_PMD_SIZE;
-				cond_resched();
-				continue;
-			}
-			if (PageAnon(*page)) {
+			if (PageAnon(*page) ||
+			    page_trans_compound_anon(*page)) {
 				flush_anon_page(vma, *page, ksm_scan.address);
 				flush_dcache_page(*page);
 				rmap_item = get_next_rmap_item(slot,