+ mm-memory-hotplug-check-folio-ref-count-first-in-do_migrate_range.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm: memory-hotplug: check folio ref count first in do_migrate_range
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-memory-hotplug-check-folio-ref-count-first-in-do_migrate_range.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-hotplug-check-folio-ref-count-first-in-do_migrate_range.patch

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

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------------------------------------------------------
From: Ma Wupeng <mawupeng1@huawei.com>
Subject: mm: memory-hotplug: check folio ref count first in do_migrate_range
Date: Mon, 17 Feb 2025 09:43:28 +0800

If a folio has an increased reference count, folio_try_get() will acquire
it, perform necessary operations, and then release it.  In the case of a
poisoned folio without an elevated reference count (which is unlikely for
memory-failure), folio_try_get() will simply bypass it.

Therefore, relocate the folio_try_get() function, responsible for checking
and acquiring this reference count at first.

Link: https://lkml.kernel.org/r/20250217014329.3610326-3-mawupeng1@huawei.com
Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory_hotplug.c |   20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

--- a/mm/memory_hotplug.c~mm-memory-hotplug-check-folio-ref-count-first-in-do_migrate_range
+++ a/mm/memory_hotplug.c
@@ -1822,12 +1822,12 @@ static void do_migrate_range(unsigned lo
 		if (folio_test_large(folio))
 			pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1;
 
-		/*
-		 * HWPoison pages have elevated reference counts so the migration would
-		 * fail on them. It also doesn't make any sense to migrate them in the
-		 * first place. Still try to unmap such a page in case it is still mapped
-		 * (keep the unmap as the catch all safety net).
-		 */
+		if (!folio_try_get(folio))
+			continue;
+
+		if (unlikely(page_folio(page) != folio))
+			goto put_folio;
+
 		if (folio_test_hwpoison(folio) ||
 		    (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) {
 			if (WARN_ON(folio_test_lru(folio)))
@@ -1835,14 +1835,8 @@ static void do_migrate_range(unsigned lo
 			if (folio_mapped(folio))
 				unmap_poisoned_folio(folio, pfn, false);
 
-			continue;
-		}
-
-		if (!folio_try_get(folio))
-			continue;
-
-		if (unlikely(page_folio(page) != folio))
 			goto put_folio;
+		}
 
 		if (!isolate_folio_to_list(folio, &source)) {
 			if (__ratelimit(&migrate_rs)) {
_

Patches currently in -mm which might be from mawupeng1@huawei.com are

mm-memory-failure-update-ttu-flag-inside-unmap_poisoned_folio.patch
mm-memory-hotplug-check-folio-ref-count-first-in-do_migrate_range.patch
hwpoison-memory_hotplug-lock-folio-before-unmap-hwpoisoned-folio.patch