memcg: fix error path of mem_cgroup_move_parent
There is a bug in error path of mem_cgroup_move_parent.
Extra refcnt got from try_charge should be dropped, and usages incremented
by try_charge should be decremented in both error paths:
A: failure at get_page_unless_zero
B: failure at isolate_lru_page
This bug makes this parent directory unremovable.
In case of A, rmdir doesn't return, because res.usage doesn't go down to 0
at mem_cgroup_force_empty even after all the pc in lru are removed.
In case of B, rmdir fails and returns -EBUSY, because it has extra ref
counts even after res.usage goes down to 0.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b665127..7be9b35 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -994,14 +994,15 @@
if (pc->mem_cgroup != from)
goto out;
- css_put(&from->css);
res_counter_uncharge(&from->res, PAGE_SIZE);
mem_cgroup_charge_statistics(from, pc, false);
if (do_swap_account)
res_counter_uncharge(&from->memsw, PAGE_SIZE);
+ css_put(&from->css);
+
+ css_get(&to->css);
pc->mem_cgroup = to;
mem_cgroup_charge_statistics(to, pc, true);
- css_get(&to->css);
ret = 0;
out:
unlock_page_cgroup(pc);
@@ -1034,8 +1035,10 @@
if (ret || !parent)
return ret;
- if (!get_page_unless_zero(page))
- return -EBUSY;
+ if (!get_page_unless_zero(page)) {
+ ret = -EBUSY;
+ goto uncharge;
+ }
ret = isolate_lru_page(page);
@@ -1044,19 +1047,23 @@
ret = mem_cgroup_move_account(pc, child, parent);
- /* drop extra refcnt by try_charge() (move_account increment one) */
- css_put(&parent->css);
putback_lru_page(page);
if (!ret) {
put_page(page);
+ /* drop extra refcnt by try_charge() */
+ css_put(&parent->css);
return 0;
}
- /* uncharge if move fails */
+
cancel:
+ put_page(page);
+uncharge:
+ /* drop extra refcnt by try_charge() */
+ css_put(&parent->css);
+ /* uncharge if move fails */
res_counter_uncharge(&parent->res, PAGE_SIZE);
if (do_swap_account)
res_counter_uncharge(&parent->memsw, PAGE_SIZE);
- put_page(page);
return ret;
}