mm: memory-hotplug: check folio ref count first in do_migrate_range

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>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: 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>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index e7e47838fd494886253a4bd95fee0184b40a6558..a6abd8d4a09c6c2de97b1d712f1b452a63be3e91 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1822,12 +1822,12 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
                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 long start_pfn, unsigned long end_pfn)
                        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)) {