Messages in this thread Patch in this message | | | Date | Thu, 8 Jan 2009 19:14:45 +0900 | From | Daisuke Nishimura <> | Subject | [RFC][PATCH 2/4] 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> --- mm/memcontrol.c | 23 +++++++++++++++-------- 1 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 62e69d8..288e22c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -983,14 +983,15 @@ 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); @@ -1023,8 +1024,10 @@ 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); @@ -1033,19 +1036,23 @@ 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; }
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