mm-damon-vaddr-do-not-repeat-pte_offset_map_lock-until-success.patch removed from -mm tree

The quilt patch titled
Subject: mm/damon/vaddr: do not repeat pte_offset_map_lock() until success
has been removed from the -mm tree. Its filename was
mm-damon-vaddr-do-not-repeat-pte_offset_map_lock-until-success.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: SeongJae Park <[email protected]>
Subject: mm/damon/vaddr: do not repeat pte_offset_map_lock() until success
Date: Mon, 29 Sep 2025 17:44:09 -0700

DAMON's virtual address space operation set implementation (vaddr) calls pte_offset_map_lock() inside the page table walk callback function. This is for reading and writing page table accessed bits. If pte_offset_map_lock() fails, it retries by returning the page table walk callback function with ACTION_AGAIN.

pte_offset_map_lock() can continuously fail if the target is a pmd migration entry, though. Hence it could cause an infinite page table walk if the migration cannot be done until the page table walk is finished. This indeed caused a soft lockup when CPU hotplugging and DAMON were running in parallel.

Avoid the infinite loop by simply not retrying the page table walk. DAMON is promising only a best-effort accuracy, so missing access to such pages is no problem.

---

 mm/damon/vaddr.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

@@ -328,10 +328,8 @@ static int damon_mkold_pmd_entry(pmd_t *
 	}
 
 	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
-	if (!pte) {
-		walk->action = ACTION_AGAIN;
+	if (!pte)
 		return 0;
-	}
 	if (!pte_present(ptep_get(pte)))
 		goto out;
 	damon_ptep_mkold(pte, walk->vma, addr);

@@ -481,10 +479,8 @@ regular_page:
 #endif	/* CONFIG_TRANSPARENT_HUGEPAGE */
 
 	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
-	if (!pte) {
-		walk->action = ACTION_AGAIN;
+	if (!pte)
 		return 0;
-	}
 	ptent = ptep_get(pte);
 	if (!pte_present(ptent))
 		goto out;

_

Patches currently in -mm which might be from [email protected] are