[PATCH v2] mm: convert partially_mapped set/clear operations to be atomic

[Usama Arif <usamaarif642@xxxxxxxxx>]

Other page flags in the 2nd page, like PG_hwpoison and
PG_anon_exclusive can get modified concurrently.
Changes to other page flags might be lost if they are
happening at the same time as non-atomic partially_mapped
operations. Hence, make partially_mapped operations atomic.

Fixes: 8422acdc97ed ("mm: introduce a pageflag for partially mapped folios")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: David Hildenbrand <david@xxxxxxxxxx>
Link: https://lore.kernel.org/all/e53b04ad-1827-43a2-a1ab-864c7efecf6e@xxxxxxxxxx/
Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
---
v1 -> v2:
- Collected acks
- Added cc for stable@xxxxxxxxxxxxxxx and link of initial report
  (Johannes)
---
 include/linux/page-flags.h | 12 ++----------
 mm/huge_memory.c           |  8 ++++----
 2 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index cf46ac720802..691506bdf2c5 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -862,18 +862,10 @@ static inline void ClearPageCompound(struct page *page)
 	ClearPageHead(page);
 }
 FOLIO_FLAG(large_rmappable, FOLIO_SECOND_PAGE)
-FOLIO_TEST_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
-/*
- * PG_partially_mapped is protected by deferred_split split_queue_lock,
- * so its safe to use non-atomic set/clear.
- */
-__FOLIO_SET_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
-__FOLIO_CLEAR_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
+FOLIO_FLAG(partially_mapped, FOLIO_SECOND_PAGE)
 #else
 FOLIO_FLAG_FALSE(large_rmappable)
-FOLIO_TEST_FLAG_FALSE(partially_mapped)
-__FOLIO_SET_FLAG_NOOP(partially_mapped)
-__FOLIO_CLEAR_FLAG_NOOP(partially_mapped)
+FOLIO_FLAG_FALSE(partially_mapped)
 #endif
 
 #define PG_head_mask ((1UL << PG_head))
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2da5520bfe24..120cd2cdc614 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3583,7 +3583,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 		    !list_empty(&folio->_deferred_list)) {
 			ds_queue->split_queue_len--;
 			if (folio_test_partially_mapped(folio)) {
-				__folio_clear_partially_mapped(folio);
+				folio_clear_partially_mapped(folio);
 				mod_mthp_stat(folio_order(folio),
 					      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			}
@@ -3695,7 +3695,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
 	if (!list_empty(&folio->_deferred_list)) {
 		ds_queue->split_queue_len--;
 		if (folio_test_partially_mapped(folio)) {
-			__folio_clear_partially_mapped(folio);
+			folio_clear_partially_mapped(folio);
 			mod_mthp_stat(folio_order(folio),
 				      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 		}
@@ -3739,7 +3739,7 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (partially_mapped) {
 		if (!folio_test_partially_mapped(folio)) {
-			__folio_set_partially_mapped(folio);
+			folio_set_partially_mapped(folio);
 			if (folio_test_pmd_mappable(folio))
 				count_vm_event(THP_DEFERRED_SPLIT_PAGE);
 			count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
@@ -3832,7 +3832,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 		} else {
 			/* We lost race with folio_put() */
 			if (folio_test_partially_mapped(folio)) {
-				__folio_clear_partially_mapped(folio);
+				folio_clear_partially_mapped(folio);
 				mod_mthp_stat(folio_order(folio),
 					      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
 			}
-- 
2.43.5