On Thu, May 26, 2016 at 04:30:18PM -0400, Tejun Heo wrote:
> 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
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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