FAILED: patch "[PATCH] mm: fix apply_to_existing_page_range()" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x a995199384347261bb3f21b2e171fa7f988bd2f8
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025042114-author-badness-6b2c@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a995199384347261bb3f21b2e171fa7f988bd2f8 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <[email protected]>
Date: Wed, 9 Apr 2025 12:40:43 +0300
Subject: [PATCH] mm: fix apply_to_existing_page_range()

In the case of apply_to_existing_page_range(), apply_to_pte_range() is reached with 'create' set to false. When !create, the loop over the PTE page table is broken.

apply_to_pte_range() will only move to the next PTE entry if 'create' is true or if the current entry is not pte_none().

This means that the user of apply_to_existing_page_range() will not have 'fn' called for any entries after the first pte_none() in the PTE page table.

Fix the loop logic in apply_to_pte_range().

There are no known runtime issues from this, but the fix is trivial enough for stable@ even without a known buggy user.

index 1a35165622e1..44481fe7c629 100644
@@ -2938,11 +2938,11 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
 	if (fn) {
 		do {
 			if (create || !pte_none(ptep_get(pte))) {
-				err = fn(pte++, addr, data);
+				err = fn(pte, addr, data);
 				if (err)
 					break;
 			}
-		} while (addr += PAGE_SIZE, addr != end);
+		} while (pte++, addr += PAGE_SIZE, addr != end);
 	}
 	*mask |= PGTBL_PTE_MODIFIED;
 

In the case of apply_to_existing_page_range(), apply_to_pte_range() is reached with 'create' set to false. When !create, the loop over the PTE page table is broken.

apply_to_pte_range() will only move to the next PTE entry if 'create' is true or if the current entry is not pte_none().

This means that the user of apply_to_existing_page_range() will not have 'fn' called for any entries after the first pte_none() in the PTE page table.

Fix the loop logic in apply_to_pte_range().

There are no known runtime issues from this, but the fix is trivial enough for stable@ even without a known buggy user.

---
 mm/memory.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 2e776ea38348..454d918449b3 100644
@@ -2659,11 +2659,11 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
 	if (fn) {
 		do {
 			if (create || !pte_none(*pte)) {
-				err = fn(pte++, addr, data);
+				err = fn(pte, addr, data);
 				if (err)
 					break;
 			}
-		} while (addr += PAGE_SIZE, addr != end);
+		} while (pte++, addr += PAGE_SIZE, addr != end);
 	}
 	*mask |= PGTBL_PTE_MODIFIED;
 

2.47.2

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
⚠️ Found matching upstream commit but patch is missing proper reference to it

Found matching upstream commit: a995199384347261bb3f21b2e171fa7f988bd2f8

Status in newer kernel trees:
6.14.y | Not found
6.12.y | Not found
6.6.y | Not found

Note: The patch differs from the upstream commit:
---
1: a995199384347 ! 1: 003668f907d5a mm: fix apply_to_existing_page_range()
@@ Commit message

+ (cherry picked from commit a995199384347261bb3f21b2e171fa7f988bd2f8)
+ Signed-off-by: Kirill A. Shutemov <[email protected]>

## mm/memory.c ##
@@ mm/memory.c: static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
if (fn) {
do {
- if (create || !pte_none(ptep_get(pte))) {
+ if (create || !pte_none(*pte)) {
- err = fn(pte++, addr, data);
+ err = fn(pte, addr, data);
if (err)
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.1.y        |  Success    |  Success   |