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memcg: fix error path of mem_cgroup_move_parent

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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>
This commit is contained in:
Daisuke Nishimura 2009-01-15 13:51:12 -08:00 committed by Linus Torvalds
parent bd112db872
commit 40d58138f8
1 changed files with 15 additions and 8 deletions
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23
mm/memcontrol.c
View File

@ -994,14 +994,15 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
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 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
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 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
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;
}