From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org,
vdavydov.dev@gmail.com, cgroups@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure
Date: Fri, 13 Apr 2018 12:35:22 +0300 [thread overview]
Message-ID: <ed75d18c-f516-2feb-53a8-6d2836e1da59@virtuozzo.com> (raw)
In-Reply-To: <20180413085553.GF17484@dhcp22.suse.cz>
On 13.04.2018 11:55, Michal Hocko wrote:
> On Thu 12-04-18 17:52:04, Kirill Tkhai wrote:
> [...]
>> @@ -4471,6 +4477,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
>>
>> return &memcg->css;
>> fail:
>> + mem_cgroup_id_remove(memcg);
>> mem_cgroup_free(memcg);
>> return ERR_PTR(-ENOMEM);
>> }
>
> The only path which jumps to fail: here (in the current mmotm tree) is
> error = memcg_online_kmem(memcg);
> if (error)
> goto fail;
>
> AFAICS and the only failure path in memcg_online_kmem
> memcg_id = memcg_alloc_cache_id();
> if (memcg_id < 0)
> return memcg_id;
>
> I am not entirely clear on memcg_alloc_cache_id but it seems we do clean
> up properly. Or am I missing something?
memcg_alloc_cache_id() may allocate a lot of memory, in case of the system reached
memcg_nr_cache_ids cgroups. In this case it iterates over all LRU lists, and double
size of every of them. In case of memory pressure it can fail. If this occurs,
mem_cgroup::id is not unhashed from IDR and we leak this id.
After further iterations, all IDs may be occupied, and there won't be able to create
a memcg in the system ever. You may reproduce the situation with the patch:
[root@localhost ~]# cd /sys/fs/cgroup/memory/
[root@localhost memory]# mkdir 1
mkdir: cannot create directory `1': Cannot allocate memory
[root@localhost memory]# for i in {1..65535}; do mkdir 1 2>/dev/null; done
[root@localhost memory]# mkdir 1
mkdir: cannot create directory `1': No space left on device
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3e7942c301a8..5e17bfee9e6f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2156,6 +2156,7 @@ static int memcg_alloc_cache_id(void)
err = memcg_update_all_caches(size);
if (!err)
err = memcg_update_all_list_lrus(size);
+ err = -ENOMEM;
if (!err)
memcg_nr_cache_ids = size;
@@ -4422,7 +4423,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
struct mem_cgroup *parent = mem_cgroup_from_css(parent_css);
struct mem_cgroup *memcg;
- long error = -ENOMEM;
+ long error = -ENOSPC;
memcg = mem_cgroup_alloc();
if (!memcg)
ENOSPC was added to the second hunk to show that the function fails on IDR allocation.
Kirill
next prev parent reply other threads:[~2018-04-13 9:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 14:52 [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure Kirill Tkhai
2018-04-13 8:55 ` Michal Hocko
2018-04-13 9:35 ` Kirill Tkhai [this message]
2018-04-13 11:02 ` Michal Hocko
2018-04-13 11:06 ` Kirill Tkhai
2018-04-13 11:20 ` Michal Hocko
2018-04-13 11:29 ` Kirill Tkhai
2018-04-13 11:38 ` Michal Hocko
2018-04-13 11:49 ` Kirill Tkhai
2018-04-13 11:54 ` Michal Hocko
2018-04-13 12:07 ` Kirill Tkhai
2018-04-13 12:14 ` Michal Hocko
2018-04-13 12:51 ` Michal Hocko
2018-07-26 23:25 ` Andrew Morton
2018-07-27 19:31 ` Johannes Weiner
2018-07-29 19:26 ` Vladimir Davydov
2018-07-30 15:31 ` Johannes Weiner
2018-07-31 23:39 ` Andrew Morton
2018-08-01 15:55 ` Johannes Weiner
2018-08-01 16:22 ` Vladimir Davydov
2018-08-02 8:03 ` Kirill Tkhai
2018-08-02 8:13 ` [PATCH] memcg: Add comment to mem_cgroup_css_online() Kirill Tkhai
2018-08-01 16:16 ` [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure Vladimir Davydov
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