From: Tejun Heo <tj@xxxxxxxxxx>
Subject: memcg: add RCU locking around css_for_each_descendant_pre() in memcg_offline_kmem()
memcg_offline_kmem() may be called from memcg_free_kmem() after a css init
failure. memcg_free_kmem() is a ->css_free callback which is called
without cgroup_mutex and memcg_offline_kmem() ends up using
css_for_each_descendant_pre() without any locking. Fix it by adding rcu
read locking around it.
mkdir: cannot create directory `65530': No space left on device
[ 527.241361] ===============================
[ 527.241845] [ INFO: suspicious RCU usage. ]
[ 527.242367] 4.6.0-work+ #321 Not tainted
[ 527.242730] -------------------------------
[ 527.243220] kernel/cgroup.c:4008 cgroup_mutex or RCU read lock required!
[ 527.243970]
[ 527.243970] other info that might help us debug this:
[ 527.243970]
[ 527.244715]
[ 527.244715] rcu_scheduler_active = 1, debug_locks = 0
[ 527.245463] 2 locks held by kworker/0:5/1664:
[ 527.245939] #0: ("cgroup_destroy"){.+.+..}, at: [<ffffffff81060ab5>] process_one_work+0x165/0x4a0
[ 527.246958] #1: ((&css->destroy_work)#3){+.+...}, at: [<ffffffff81060ab5>] process_one_work+0x165/0x4a0
[ 527.248098]
[ 527.248098] stack backtrace:
[ 527.249565] CPU: 0 PID: 1664 Comm: kworker/0:5 Not tainted 4.6.0-work+ #321
[ 527.250429] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 04/01/2014
[ 527.250555] Workqueue: cgroup_destroy css_free_work_fn
[ 527.250555] 0000000000000000 ffff880178747c68 ffffffff8128bfc7 ffff880178b8ac40
[ 527.250555] 0000000000000001 ffff880178747c98 ffffffff8108c297 0000000000000000
[ 527.250555] ffff88010de54138 000000000000fffb ffff88010de537e8 ffff880178747cc0
[ 527.250555] Call Trace:
[ 527.250555] [<ffffffff8128bfc7>] dump_stack+0x68/0xa1
[ 527.250555] [<ffffffff8108c297>] lockdep_rcu_suspicious+0xd7/0x110
[ 527.250555] [<ffffffff810ca03d>] css_next_descendant_pre+0x7d/0xb0
[ 527.250555] [<ffffffff8114d14a>] memcg_offline_kmem.part.44+0x4a/0xc0
[ 527.250555] [<ffffffff8114d3ac>] mem_cgroup_css_free+0x1ec/0x200
[ 527.250555] [<ffffffff810ccdc9>] css_free_work_fn+0x49/0x5e0
[ 527.250555] [<ffffffff81060b15>] process_one_work+0x1c5/0x4a0
[ 527.250555] [<ffffffff81060ab5>] ? process_one_work+0x165/0x4a0
[ 527.250555] [<ffffffff81060e39>] worker_thread+0x49/0x490
[ 527.250555] [<ffffffff81060df0>] ? process_one_work+0x4a0/0x4a0
[ 527.250555] [<ffffffff81060df0>] ? process_one_work+0x4a0/0x4a0
[ 527.250555] [<ffffffff810672ba>] kthread+0xea/0x100
[ 527.250555] [<ffffffff814cbcff>] ret_from_fork+0x1f/0x40
[ 527.250555] [<ffffffff810671d0>] ? kthread_create_on_node+0x200/0x200
Link: http://lkml.kernel.org/r/20160526203018.GG23194@xxxxxxxxxxxxxxx
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.5+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN mm/memcontrol.c~memcg-add-rcu-locking-around-css_for_each_descendant_pre-in-memcg_offline_kmem mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-add-rcu-locking-around-css_for_each_descendant_pre-in-memcg_offline_kmem
+++ a/mm/memcontrol.c
@@ -2896,6 +2896,7 @@ static void memcg_offline_kmem(struct me
* ordering is imposed by list_lru_node->lock taken by
* memcg_drain_all_list_lrus().
*/
+ rcu_read_lock(); /* can be called from css_free w/o cgroup_mutex */
css_for_each_descendant_pre(css, &memcg->css) {
child = mem_cgroup_from_css(css);
BUG_ON(child->kmemcg_id != kmemcg_id);
@@ -2903,6 +2904,8 @@ static void memcg_offline_kmem(struct me
if (!memcg->use_hierarchy)
break;
}
+ rcu_read_unlock();
+
memcg_drain_all_list_lrus(kmemcg_id, parent->kmemcg_id);
memcg_free_cache_id(kmemcg_id);
_
--
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