INFO: task kworker/u4:1:19 blocked for more than 120 seconds.
      Not tainted 4.4.107-g610c835 #12
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:1    D ffff8801da3ff8b8 24920    19      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801da3ff8b8 dffffc0000000000 ffff8801da3237f0 ffff8801da3ff898
 ffffffff8123364f ffff8801da323700 ffff8801db31f878 ffff8801db31f8a0
 ffff8801db31ef98 ffff8801cccbdf00 ffff8801da322f80 ffff8801da3f8000
Call Trace:
 [<ffffffff83765d3a>] schedule+0x9a/0x1c0 kernel/sched/core.c:3351
 [<ffffffff8376ffef>] rwsem_down_read_failed+0x1bf/0x300 kernel/locking/rwsem-xadd.c:250
 [<ffffffff81d34e44>] call_rwsem_down_read_failed+0x14/0x30 arch/x86/lib/rwsem.S:90
 [<ffffffff81f56944>] n_tty_receive_buf_common+0x84/0x21c0 drivers/tty/n_tty.c:1705
 [<ffffffff81f58ab3>] n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1777
 [<ffffffff81f61acb>] receive_buf drivers/tty/tty_buffer.c:451 [inline]
 [<ffffffff81f61acb>] flush_to_ldisc+0x27b/0x4a0 drivers/tty/tty_buffer.c:516
 [<ffffffff8117d3f7>] process_one_work+0x7d7/0x16e0 kernel/workqueue.c:2064
 [<ffffffff8117e3df>] worker_thread+0xdf/0xfe0 kernel/workqueue.c:2196
 [<ffffffff8118dea8>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff837740ef>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468