Commit 4bdfc1c4 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds

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-00501b53 ("mm: memcontrol: rewrite charge API") era.  Remove it
to fix the leak.

Fixes: e8ea14cc (mm: memcontrol: take a css reference for each charged page)
Signed-off-by: default avatarVladimir Davydov <>
Cc: Johannes Weiner <>
Acked-by: default avatarMichal Hocko <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 24d404dc
......@@ -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().
return 0;
return -EINVAL;
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment