4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tejun Heo <tj@xxxxxxxxxx>
commit 3a06bb78ceeceacc86a1e31133a7944013f9775b upstream.
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
===============================
[ INFO: suspicious RCU usage. ]
4.6.0-work+ #321 Not tainted
-------------------------------
kernel/cgroup.c:4008 cgroup_mutex or RCU read lock required!
[ 527.243970] other info that might help us debug this:
[ 527.244715]
rcu_scheduler_active = 1, debug_locks = 0
2 locks held by kworker/0:5/1664:
#0: ("cgroup_destroy"){.+.+..}, at: [<ffffffff81060ab5>] process_one_work+0x165/0x4a0
#1: ((&css->destroy_work)#3){+.+...}, at: [<ffffffff81060ab5>] process_one_work+0x165/0x4a0
[ 527.248098] stack backtrace:
CPU: 0 PID: 1664 Comm: kworker/0:5 Not tainted 4.6.0-work+ #321
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 04/01/2014
Workqueue: cgroup_destroy css_free_work_fn
Call Trace:
dump_stack+0x68/0xa1
lockdep_rcu_suspicious+0xd7/0x110
css_next_descendant_pre+0x7d/0xb0
memcg_offline_kmem.part.44+0x4a/0xc0
mem_cgroup_css_free+0x1ec/0x200
css_free_work_fn+0x49/0x5e0
process_one_work+0x1c5/0x4a0
worker_thread+0x49/0x490
kthread+0xea/0x100
ret_from_fork+0x1f/0x40
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 3 +++
1 file changed, 3 insertions(+)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3661,6 +3661,7 @@ static void memcg_deactivate_kmem(struct
* 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);
@@ -3668,6 +3669,8 @@ static void memcg_deactivate_kmem(struct
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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