[PATCH -next] mm/ksm: Add missing IS_ERR_OR_NULL check for stable_tree_search()

[Gaosheng Cui <cuigaosheng1@huawei.com>]

The stable_tree_search() maybe return -EBUSY if the stable node's page
is being migrated or nullptr, we need to check kfolio with
IS_ERR_OR_NULL() before dereference it.

To mitigate this, add IS_ERR_OR_NULL check for stable_tree_search().

Fixes: 15605244fdce ("ksm: convert cmp_and_merge_page() to use a folio")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
---
 mm/ksm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 4d482d011745..7ac59cde626c 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1787,7 +1787,7 @@ static __always_inline struct folio *chain(struct ksm_stable_node **s_n_d,
  * with identical content to the page that we are scanning right now.
  *
  * This function returns the stable tree node of identical content if found,
- * NULL otherwise.
+ * -EBUSY if the stable node's page is being migrated, NULL otherwise.
  */
 static struct folio *stable_tree_search(struct page *page)
 {
@@ -2261,7 +2261,8 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 
 	/* Start by searching for the folio in the stable tree */
 	kfolio = stable_tree_search(page);
-	if (&kfolio->page == page && rmap_item->head == stable_node) {
+	if (!IS_ERR_OR_NULL(kfolio) && &kfolio->page == page &&
+	    rmap_item->head == stable_node) {
 		folio_put(kfolio);
 		return;
 	}
-- 
2.25.1