[PATCH] mm: memcontrol: fix swap counter leak from offline cgroup

[Muchun Song <songmuchun@xxxxxxxxxxxxx>]

The commit 6769183166b3 has removed the parameter of id from
swap_cgroup_record() and get the memcg id from
mem_cgroup_id(folio_memcg(folio)). However, the caller of it
may update a different memcg's counter instead of
folio_memcg(folio). E.g. in the caller of mem_cgroup_swapout(),
@swap_memcg could be different with @memcg and update the counter
of @swap_memcg, but swap_cgroup_record() records the wrong memcg's
ID. When it is uncharged from __mem_cgroup_uncharge_swap(), the
swap counter will leak since the wrong recorded ID. Fix it by
bring the parameter of id back.

Fixes: 6769183166b3 ("mm/swap_cgroup: decouple swap cgroup recording and clearing")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 include/linux/swap_cgroup.h | 4 ++--
 mm/memcontrol.c             | 4 ++--
 mm/swap_cgroup.c            | 7 ++++---
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/linux/swap_cgroup.h b/include/linux/swap_cgroup.h
index b5ec038069dab..91cdf12190a03 100644
--- a/include/linux/swap_cgroup.h
+++ b/include/linux/swap_cgroup.h
@@ -6,7 +6,7 @@
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_SWAP)
 
-extern void swap_cgroup_record(struct folio *folio, swp_entry_t ent);
+extern void swap_cgroup_record(struct folio *folio, unsigned short id, swp_entry_t ent);
 extern unsigned short swap_cgroup_clear(swp_entry_t ent, unsigned int nr_ents);
 extern unsigned short lookup_swap_cgroup_id(swp_entry_t ent);
 extern int swap_cgroup_swapon(int type, unsigned long max_pages);
@@ -15,7 +15,7 @@ extern void swap_cgroup_swapoff(int type);
 #else
 
 static inline
-void swap_cgroup_record(struct folio *folio, swp_entry_t ent)
+void swap_cgroup_record(struct folio *folio, unsigned short id, swp_entry_t ent)
 {
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a5d870fbb4321..a5ab603806fbb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4988,7 +4988,7 @@ void mem_cgroup_swapout(struct folio *folio, swp_entry_t entry)
 		mem_cgroup_id_get_many(swap_memcg, nr_entries - 1);
 	mod_memcg_state(swap_memcg, MEMCG_SWAP, nr_entries);
 
-	swap_cgroup_record(folio, entry);
+	swap_cgroup_record(folio, mem_cgroup_id(swap_memcg), entry);
 
 	folio_unqueue_deferred_split(folio);
 	folio->memcg_data = 0;
@@ -5050,7 +5050,7 @@ int __mem_cgroup_try_charge_swap(struct folio *folio, swp_entry_t entry)
 		mem_cgroup_id_get_many(memcg, nr_pages - 1);
 	mod_memcg_state(memcg, MEMCG_SWAP, nr_pages);
 
-	swap_cgroup_record(folio, entry);
+	swap_cgroup_record(folio, mem_cgroup_id(memcg), entry);
 
 	return 0;
 }
diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index be39078f255be..1007c30f12e2c 100644
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -58,9 +58,11 @@ static unsigned short __swap_cgroup_id_xchg(struct swap_cgroup *map,
  * entries must not have been charged
  *
  * @folio: the folio that the swap entry belongs to
+ * @id: mem_cgroup ID to be recorded
  * @ent: the first swap entry to be recorded
  */
-void swap_cgroup_record(struct folio *folio, swp_entry_t ent)
+void swap_cgroup_record(struct folio *folio, unsigned short id,
+			swp_entry_t ent)
 {
 	unsigned int nr_ents = folio_nr_pages(folio);
 	struct swap_cgroup *map;
@@ -72,8 +74,7 @@ void swap_cgroup_record(struct folio *folio, swp_entry_t ent)
 	map = swap_cgroup_ctrl[swp_type(ent)].map;
 
 	do {
-		old = __swap_cgroup_id_xchg(map, offset,
-					    mem_cgroup_id(folio_memcg(folio)));
+		old = __swap_cgroup_id_xchg(map, offset, id);
 		VM_BUG_ON(old);
 	} while (++offset != end);
 }
-- 
2.20.1