Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure

Andrew Morton
2018-07-26T23:25:17Z

On Fri, 13 Apr 2018 14:51:01 +0200 Michal Hocko <mhocko@kernel.org> wrote:

> On Fri 13-04-18 14:14:33, Michal Hocko wrote:
> [...]
> > Well, this is probably a matter of taste. I will not argue. I will not
> > object if Johannes is OK with your patch. But the whole thing confused
> > hell out of me so I would rather un-clutter it...
>
> In other words, this
>

This discussion has rather petered out. afaict we're waiting for
hannes to offer an opinion?

From: Kirill Tkhai <ktkhai@virtuozzo.com>
Subject: memcg: remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure

In case of memcg_online_kmem() failure, memcg_cgroup::id remains hashed in
mem_cgroup_idr even after memcg memory is freed. This leads to leak of ID
in mem_cgroup_idr.

This patch adds removal into mem_cgroup_css_alloc(), which fixes the
problem. For better readability, it adds a generic helper which is used
in mem_cgroup_alloc() and mem_cgroup_id_put_many() as well.

Link: http://lkml.kernel.org/r/152354470916.22460.14397070748001974638.stgit@localhost.localdomain
Fixes 73f576c04b94 ("mm: memcontrol: fix cgroup creation failure after many small jobs")
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/memcontrol.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff -puN mm/memcontrol.c~memcg-remove-memcg_cgroup-id-from-idr-on-mem_cgroup_css_alloc-failure mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-remove-memcg_cgroup-id-from-idr-on-mem_cgroup_css_alloc-failure
+++ a/mm/memcontrol.c
@@ -4037,6 +4037,14 @@ static struct cftype mem_cgroup_legacy_f

static DEFINE_IDR(mem_cgroup_idr);

+static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
+{
+ if (memcg->id.id > 0) {
+ idr_remove(&mem_cgroup_idr, memcg->id.id);
+ memcg->id.id = 0;
+ }
+}
+
static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
{
VM_BUG_ON(atomic_read(&memcg->id.ref) <= 0);
@@ -4047,8 +4055,7 @@ static void mem_cgroup_id_put_many(struc
{
VM_BUG_ON(atomic_read(&memcg->id.ref) < n);
if (atomic_sub_and_test(n, &memcg->id.ref)) {
- idr_remove(&mem_cgroup_idr, memcg->id.id);
- memcg->id.id = 0;
+ mem_cgroup_id_remove(memcg);

/* Memcg ID pins CSS */
css_put(&memcg->css);
@@ -4185,8 +4192,7 @@ static struct mem_cgroup *mem_cgroup_all
idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
return memcg;
fail:
- if (memcg->id.id > 0)
- idr_remove(&mem_cgroup_idr, memcg->id.id);
+ mem_cgroup_id_remove(memcg);
__mem_cgroup_free(memcg);
return NULL;
}
@@ -4245,6 +4251,7 @@ mem_cgroup_css_alloc(struct cgroup_subsy

return &memcg->css;
fail:
+ mem_cgroup_id_remove(memcg);
mem_cgroup_free(memcg);
return ERR_PTR(-ENOMEM);
}
_