Commit 4bdfc1c4 authored Jan 08, 2015 by Vladimir Davydov Committed by Linus Torvalds Jan 08, 2015

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: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 24d404dc

mm/memcontrol.c

+0 −12

Original line number	Diff line number	Diff line
		@@ -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;

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