[lkml]   [2014]   [Dec]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH] memcg: fix destination cgroup leak on task charges migration
We are supposed to take one css reference per each memory page and per
each swap entry accounted to a memory cgroup. However, during task
charges migration we take a reference to the destination cgroup twice
per each swap entry: first in mem_cgroup_do_precharge()->try_charge()
and then in mem_cgroup_move_swap_account(), permanently leaking the
destination cgroup.

The hunk taking the second reference seems to be a leftover from the
pre-00501b531c472 ("mm: memcontrol: rewrite charge API") era. Remove it
to fix the leak.

Signed-off-by: Vladimir Davydov <>
mm/memcontrol.c | 12 ------------
1 file changed, 12 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ef91e856c7e4..d62c335dfef4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3043,18 +3043,6 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
mem_cgroup_swap_statistics(from, false);
mem_cgroup_swap_statistics(to, true);
- /*
- * This function is only called from task migration context now.
- * It postpones page_counter and refcount handling till the end
- * of task migration(mem_cgroup_clear_mc()) for performance
- * improvement. But we cannot postpone css_get(to) because if
- * the process that has been moved to @to does swap-in, the
- * refcount of @to might be decreased to 0.
- *
- * We are in attach() phase, so the cgroup is guaranteed to be
- * alive, so we can just call css_get().
- */
- css_get(&to->css);
return 0;
return -EINVAL;

 \ /
  Last update: 2014-12-29 17:01    [W:0.034 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site