INFO: task docker:20744 blocked for more than 120 seconds.
      Tainted: G         C    3.16.0-4-amd64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
docker          D ffff8801a8f2b078     0 20744      1 0x00000000
 ffff8801a8f2ac20 0000000000000082 0000000000012f00 ffff880057a17fd8
 0000000000012f00 ffff8801a8f2ac20 ffffffff818bb4a0 ffff880057a17d80
 ffffffff818bb4a4 ffff8801a8f2ac20 00000000ffffffff ffffffff818bb4a8
Call Trace:
 [<ffffffff81510915>] ? schedule_preempt_disabled+0x25/0x70
 [<ffffffff815123c3>] ? __mutex_lock_slowpath+0xd3/0x1c0
 [<ffffffff815124cb>] ? mutex_lock+0x1b/0x2a
 [<ffffffff814175bc>] ? copy_net_ns+0x6c/0x130
 [<ffffffff8108bdf4>] ? create_new_namespaces+0xf4/0x180
 [<ffffffff8108beec>] ? copy_namespaces+0x6c/0x90
 [<ffffffff810654f6>] ? copy_process.part.25+0x966/0x1c30
 [<ffffffff81066991>] ? do_fork+0xe1/0x390
 [<ffffffff811c442c>] ? __alloc_fd+0x7c/0x120
 [<ffffffff81514079>] ? stub_clone+0x69/0x90
 [<ffffffff81513d0d>] ? system_call_fast_compare_end+0x10/0x15