INFO: task kworker/u4:0:6 blocked for more than 120 seconds.
      Not tainted 4.9.71-g2506378 #113
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:0    D26384     6      2 0x00000000
Workqueue: events_unbound flush_to_ldisc
 ffff8801da290000 ffff8801c50d7480 ffff8801c50d7480 ffff8801c3b70000
 ffff8801db221458 ffff8801da29f850 ffffffff8389e00b ffff8801da29f828
 ffffffff8123940f 00ffffff838a997a ffff8801db221d28 ffff8801db221d50
Call Trace:
 [<ffffffff8389f5af>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838a9a90>] rwsem_down_read_failed+0x1e0/0x320 kernel/locking/rwsem-xadd.c:260
 [<ffffffff81dc5448>] call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
 [<ffffffff838a8812>] __down_read arch/x86/include/asm/rwsem.h:65 [inline]
 [<ffffffff838a8812>] down_read+0x52/0xb0 kernel/locking/rwsem.c:24