4.15.0-43-generic #46~16.04.1-Ubuntu SMP x86_64

I have the same problem but the process that gets stuck is dockerd not systemd.

3,2077,80354225063,-;INFO: task dockerd:2070 blocked for more than 120 seconds.
3,2078,80354230430,-;      Tainted: P           O     4.15.0-43-generic #46~16.04.1-Ubuntu
3,2079,80354236566,-;"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
6,2080,80354242978,-;dockerd         D    0  2070      1 0x00000000
4,2081,80354242981,-;Call Trace:
4,2082,80354242984,-; __schedule+0x3d6/0x8b0
4,2083,80354242986,-; ? xen_smp_send_reschedule+0x10/0x20
4,2084,80354242989,-; schedule+0x36/0x80
4,2085,80354242991,-; schedule_timeout+0x1db/0x370
4,2086,80354242993,-; ? try_to_wake_up+0x59/0x4a0
4,2087,80354242995,-; wait_for_completion+0xb4/0x140
4,2088,80354242996,-; ? wake_up_q+0x70/0x70
4,2089,80354242998,-; flush_work+0x129/0x1e0
4,2090,80354242999,-; ? worker_detach_from_pool+0xb0/0xb0
4,2091,80354243001,-; flush_delayed_work+0x3f/0x50
4,2092,80354243004,-; fsnotify_wait_marks_destroyed+0x15/0x20
4,2093,80354243005,-; fsnotify_destroy_group+0x48/0xd0
4,2094,80354243008,-; inotify_release+0x1e/0x50
4,2095,80354243011,-; __fput+0xea/0x220
4,2096,80354243013,-; ____fput+0xe/0x10
4,2097,80354243014,-; task_work_run+0x8a/0xb0
4,2098,80354243016,-; exit_to_usermode_loop+0xc4/0xd0
4,2099,80354243018,-; do_syscall_64+0xf4/0x130
4,2100,80354243020,-; entry_SYSCALL_64_after_hwframe+0x3d/0xa2

The tainted marker is from zfs module since I have a ZFS partition mounted in the system.
The / partition however is EXT4, and docker is running from /.

cat /proc/1/stack
[<0>] flush_work+0x129/0x1e0
[<0>] flush_delayed_work+0x3f/0x50
[<0>] fsnotify_wait_marks_destroyed+0x15/0x20
[<0>] fsnotify_destroy_group+0x48/0xd0
[<0>] inotify_release+0x1e/0x50
[<0>] __fput+0xea/0x220
[<0>] ____fput+0xe/0x10
[<0>] task_work_run+0x8a/0xb0
[<0>] exit_to_usermode_loop+0xc4/0xd0
[<0>] do_syscall_64+0xf4/0x130
[<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[<0>] 0xffffffffffffffff


6,2111,218820611653,-;  task                        PC stack   pid father
6,2112,218820614372,-;systemd         D    0     1      0 0x00000004
4,2113,218820616975,-;Call Trace:
4,2114,218820618224,-; __schedule+0x3d6/0x8b0
4,2115,218820619977,-; ? xen_smp_send_reschedule+0x10/0x20
4,2116,218820622101,-; schedule+0x36/0x80
4,2117,218820624470,-; schedule_timeout+0x1db/0x370
4,2118,218820627660,-; ? delete_node+0x1a5/0x1f0
4,2119,218820630763,-; wait_for_completion+0xb4/0x140
4,2120,218820634184,-; ? wake_up_q+0x70/0x70
4,2121,218820638148,-; flush_work+0x129/0x1e0
4,2122,218820642490,-; ? worker_detach_from_pool+0xb0/0xb0
4,2123,218820646706,-; flush_delayed_work+0x3f/0x50
4,2124,218820650474,-; fsnotify_wait_marks_destroyed+0x15/0x20
4,2125,218820654789,-; fsnotify_destroy_group+0x48/0xd0
4,2126,218820658838,-; inotify_release+0x1e/0x50
4,2127,218820662400,-; __fput+0xea/0x220
4,2128,218820665486,-; ____fput+0xe/0x10
4,2129,218820668890,-; task_work_run+0x8a/0xb0
4,2130,218820672633,-; exit_to_usermode_loop+0xc4/0xd0
4,2131,218820676852,-; do_syscall_64+0xf4/0x130
4,2132,218820680778,-; entry_SYSCALL_64_after_hwframe+0x3d/0xa2
4,2133,218820686587,-;RIP: 0033:0x7efd22aaf57d
4,2134,218820691555,-;RSP: 002b:00007ffd463e6070 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
4,2135,218820699907,-;RAX: 0000000000000000 RBX: 000000000000000d RCX: 00007efd22aaf57d
4,2136,218820708355,-;RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000000000d
4,2137,218820717053,-;RBP: 00007efd241ea708 R08: 00005559085084d0 R09: 0000000000000001
4,2138,218820726163,-;R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000002
4,2139,218820734459,-;R13: 000055590749d580 R14: 00005559084bd9b8 R15: 000055590749e9c0


Also kworker shows a stack at some point.

3,1861,80233315906,-;INFO: task kworker/u30:3:5705 blocked for more than 120 seconds.
3,1862,80233321444,-;      Tainted: P           O     4.15.0-43-generic #46~16.04.1-Ubuntu
3,1863,80233327648,-;"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
6,1864,80233333902,-;kworker/u30:3   D    0  5705      2 0x80000000
6,1865,80233333909,-;Workqueue: events_unbound fsnotify_mark_destroy_workfn
4,1866,80233333910,-;Call Trace:
4,1867,80233333914,-; __schedule+0x3d6/0x8b0
4,1868,80233333918,-; schedule+0x36/0x80
4,1869,80233333920,-; schedule_timeout+0x1db/0x370
4,1870,80233333927,-; ? __enqueue_entity+0x5c/0x60
4,1871,80233333932,-; ? enqueue_entity+0x112/0x670
4,1872,80233333937,-; wait_for_completion+0xb4/0x140
4,1873,80233333939,-; ? wake_up_q+0x70/0x70
4,1874,80233333944,-; __synchronize_srcu.part.13+0x85/0xb0
4,1875,80233333947,-; ? trace_raw_output_rcu_utilization+0x50/0x50
4,1876,80233333950,-; synchronize_srcu+0xd3/0xe0
4,1877,80233333956,-; ? synchronize_srcu+0xd3/0xe0
4,1878,80233333962,-; fsnotify_mark_destroy_workfn+0x7c/0xe0
4,1879,80233333966,-; process_one_work+0x14d/0x410
4,1880,80233333968,-; worker_thread+0x22b/0x460
4,1881,80233333971,-; kthread+0x105/0x140
4,1882,80233333974,-; ? process_one_work+0x410/0x410
4,1883,80233333976,-; ? kthread_destroy_worker+0x50/0x50
4,1884,80233333979,-; ret_from_fork+0x35/0x40

A note on this is that the issues reappears after a reboot either in a day or in a few days.