diff options
authorHugh Dickins <>2020-07-24 07:15:24 +0300
committerLinus Torvalds <>2020-07-24 22:42:41 +0300
commit8d22a9351035ef2ff12ef163a1091b8b8cf1e49c (patch)
parent82ff165cd35110d4e380b55927bbd74dcb564998 (diff)
mm/memcg: fix refcount error while moving and swapping
It was hard to keep a test running, moving tasks between memcgs with move_charge_at_immigrate, while swapping: mem_cgroup_id_get_many()'s refcount is discovered to be 0 (supposedly impossible), so it is then forced to REFCOUNT_SATURATED, and after thousands of warnings in quick succession, the test is at last put out of misery by being OOM killed. This is because of the way moved_swap accounting was saved up until the task move gets completed in __mem_cgroup_clear_mc(), deferred from when mem_cgroup_move_swap_account() actually exchanged old and new ids. Concurrent activity can free up swap quicker than the task is scanned, bringing id refcount down 0 (which should only be possible when offlining). Just skip that optimization: do that part of the accounting immediately. Fixes: 615d66c37c75 ("mm: memcontrol: fix memcg id ref counter on swap charge move") Signed-off-by: Hugh Dickins <> Signed-off-by: Andrew Morton <> Reviewed-by: Alex Shi <> Cc: Johannes Weiner <> Cc: Alex Shi <> Cc: Shakeel Butt <> Cc: Michal Hocko <> Cc: <> Link: Signed-off-by: Linus Torvalds <>
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c75c4face02e..13f559af1ab6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5669,7 +5669,6 @@ static void __mem_cgroup_clear_mc(void)
if (!mem_cgroup_is_root(
page_counter_uncharge(&>memory, mc.moved_swap);
- mem_cgroup_id_get_many(, mc.moved_swap);
css_put_many(&>css, mc.moved_swap);
mc.moved_swap = 0;
@@ -5860,7 +5859,8 @@ put: /* get_mctgt_type() gets the page */
ent = target.ent;
if (!mem_cgroup_move_swap_account(ent, mc.from, {
- /* we fixup refcnts and charges later. */
+ mem_cgroup_id_get_many(, 1);
+ /* we fixup other refcnts and charges later. */