1 files changed, 35 insertions, 10 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 983fbac24bda..fc64874dc6f4 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -667,6 +667,12 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
 	free_stable_node(stable_node);
 }
 
+enum get_ksm_page_flags {
+	GET_KSM_PAGE_NOLOCK,
+	GET_KSM_PAGE_LOCK,
+	GET_KSM_PAGE_TRYLOCK
+};
+
 /*
  * get_ksm_page: checks if the page indicated by the stable node
  * is still its ksm page, despite having held no reference to it.
@@ -686,7 +692,8 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
  * a page to put something that might look like our key in page->mapping.
  * is on its way to being freed; but it is an anomaly to bear in mind.
  */
-static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
+static struct page *get_ksm_page(struct stable_node *stable_node,
+				 enum get_ksm_page_flags flags)
 {
 	struct page *page;
 	void *expected_mapping;
@@ -729,8 +736,15 @@ again:
 		goto stale;
 	}
 
-	if (lock_it) {
+	if (flags == GET_KSM_PAGE_TRYLOCK) {
+		if (!trylock_page(page)) {
+			put_page(page);
+			return ERR_PTR(-EBUSY);
+		}
+	} else if (flags == GET_KSM_PAGE_LOCK)
 		lock_page(page);
+
+	if (flags != GET_KSM_PAGE_NOLOCK) {
 		if (READ_ONCE(page->mapping) != expected_mapping) {
 			unlock_page(page);
 			put_page(page);
@@ -764,7 +778,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 		struct page *page;
 
 		stable_node = rmap_item->head;
-		page = get_ksm_page(stable_node, true);
+		page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
 		if (!page)
 			goto out;
 
@@ -864,7 +878,7 @@ static int remove_stable_node(struct stable_node *stable_node)
 	struct page *page;
 	int err;
 
-	page = get_ksm_page(stable_node, true);
+	page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
 	if (!page) {
 		/*
 		 * get_ksm_page did remove_node_from_stable_tree itself.
@@ -1386,7 +1400,7 @@ static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
 		 * stable_node parameter itself will be freed from
 		 * under us if it returns NULL.
 		 */
-		_tree_page = get_ksm_page(dup, false);
+		_tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
 		if (!_tree_page)
 			continue;
 		nr += 1;
@@ -1509,7 +1523,7 @@ static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
 	if (!is_stable_node_chain(stable_node)) {
 		if (is_page_sharing_candidate(stable_node)) {
 			*_stable_node_dup = stable_node;
-			return get_ksm_page(stable_node, false);
+			return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
 		}
 		/*
 		 * _stable_node_dup set to NULL means the stable_node
@@ -1614,7 +1628,8 @@ again:
 			 * wrprotected at all times. Any will work
 			 * fine to continue the walk.
 			 */
-			tree_page = get_ksm_page(stable_node_any, false);
+			tree_page = get_ksm_page(stable_node_any,
+						 GET_KSM_PAGE_NOLOCK);
 		}
 		VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
 		if (!tree_page) {
@@ -1674,7 +1689,12 @@ again:
 			 * It would be more elegant to return stable_node
 			 * than kpage, but that involves more changes.
 			 */
-			tree_page = get_ksm_page(stable_node_dup, true);
+			tree_page = get_ksm_page(stable_node_dup,
+						 GET_KSM_PAGE_TRYLOCK);
+
+			if (PTR_ERR(tree_page) == -EBUSY)
+				return ERR_PTR(-EBUSY);
+
 			if (unlikely(!tree_page))
 				/*
 				 * The tree may have been rebalanced,
@@ -1843,7 +1863,8 @@ again:
 			 * wrprotected at all times. Any will work
 			 * fine to continue the walk.
 			 */
-			tree_page = get_ksm_page(stable_node_any, false);
+			tree_page = get_ksm_page(stable_node_any,
+						 GET_KSM_PAGE_NOLOCK);
 		}
 		VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
 		if (!tree_page) {
@@ -2069,6 +2090,9 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
 	remove_rmap_item_from_tree(rmap_item);
 
 	if (kpage) {
+		if (PTR_ERR(kpage) == -EBUSY)
+			return;
+
 		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
 		if (!err) {
 			/*
@@ -2243,7 +2267,8 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
 
 			list_for_each_entry_safe(stable_node, next,
 						 &migrate_nodes, list) {
-				page = get_ksm_page(stable_node, false);
+				page = get_ksm_page(stable_node,
+						    GET_KSM_PAGE_NOLOCK);
 				if (page)
 					put_page(page);
 				cond_resched();