+ ksm-convert-cmp_and_merge_page-to-use-a-folio-fix.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/ksm: add missing IS_ERR_OR_NULL check for stable_tree_search()
has been added to the -mm mm-unstable branch.  Its filename is
     ksm-convert-cmp_and_merge_page-to-use-a-folio-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ksm-convert-cmp_and_merge_page-to-use-a-folio-fix.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Gaosheng Cui <cuigaosheng1@huawei.com>
Subject: mm/ksm: add missing IS_ERR_OR_NULL check for stable_tree_search()
Date: Thu, 24 Oct 2024 11:23:00 +0800

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().

Link: https://lkml.kernel.org/r/20241024032300.2501949-1-cuigaosheng1@huawei.com
Fixes: ("ksm: convert cmp_and_merge_page() to use a folio")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/ksm.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/ksm.c~ksm-convert-cmp_and_merge_page-to-use-a-folio-fix
+++ a/mm/ksm.c
@@ -1787,7 +1787,7 @@ static __always_inline struct folio *cha
  * 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 pa
 
 	/* 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;
 	}
_

Patches currently in -mm which might be from cuigaosheng1@huawei.com are

ksm-convert-cmp_and_merge_page-to-use-a-folio-fix.patch