Comment 5 for bug 1798212

On 18.04 with kernel 4.15.0-46-generic #49-Ubuntu we hit the hang:

[Apr25 10:10] INFO: task kworker/u256:3:48574 blocked for more than 120 seconds.
[ +0.000106] Not tainted 4.15.0-46-generic #49-Ubuntu
[ +0.000017] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ +0.000023] kworker/u256:3 D 0 48574 2 0x80000000
[ +0.000009] Workqueue: events_unbound fsnotify_mark_destroy_workfn
[ +0.000001] Call Trace:
[ +0.000007] __schedule+0x291/0x8a0
[ +0.000002] schedule+0x2c/0x80
[ +0.000002] schedule_timeout+0x1cf/0x350
[ +0.000003] ? select_idle_sibling+0x29/0x410
[ +0.000002] ? __enqueue_entity+0x5c/0x60
[ +0.000002] ? enqueue_entity+0x10e/0x6b0
[ +0.000002] wait_for_completion+0xba/0x140
[ +0.000001] ? wake_up_q+0x80/0x80
[ +0.000004] __synchronize_srcu.part.13+0x85/0xb0
[ +0.000002] ? trace_raw_output_rcu_utilization+0x50/0x50
[ +0.000001] ? ttwu_do_activate+0x77/0x80
[ +0.000002] synchronize_srcu+0x66/0xe0
[ +0.000001] ? synchronize_srcu+0x66/0xe0
[ +0.000002] fsnotify_mark_destroy_workfn+0x7b/0xe0
[ +0.000003] process_one_work+0x1de/0x410
[ +0.000001] worker_thread+0x228/0x410
[ +0.000002] kthread+0x121/0x140
[ +0.000001] ? process_one_work+0x410/0x410
[ +0.000002] ? kthread_create_worker_on_cpu+0x70/0x70
[ +0.000003] ? do_syscall_64+0x73/0x130
[ +0.000002] ? SyS_exit_group+0x14/0x20
[ +0.000002] ret_from_fork+0x35/0x40
[ +0.000008] INFO: task systemd:50609 blocked for more than 120 seconds.
[ +0.000021] Not tainted 4.15.0-46-generic #49-Ubuntu
[ +0.000016] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ +0.000021] systemd D 0 50609 1 0x00000004
[ +0.000002] Call Trace:
[ +0.000002] __schedule+0x291/0x8a0
[ +0.000002] ? sock_def_readable+0x40/0x70
[ +0.000003] ? unix_dgram_sendmsg+0x356/0x6f0
[ +0.000001] schedule+0x2c/0x80
[ +0.000002] schedule_timeout+0x1cf/0x350
[ +0.000003] ? __radix_tree_delete+0x7f/0xa0
[ +0.000001] wait_for_completion+0xba/0x140
[ +0.000001] ? wake_up_q+0x80/0x80
[ +0.000002] flush_work+0x126/0x1e0
[ +0.000001] ? worker_detach_from_pool+0xa0/0xa0
[ +0.000002] flush_delayed_work+0x3f/0x50
[ +0.000002] fsnotify_wait_marks_destroyed+0x15/0x20
[ +0.000001] fsnotify_destroy_group+0x48/0xd0
[ +0.000002] inotify_release+0x1e/0x50
[ +0.000003] __fput+0xea/0x220
[ +0.000001] ____fput+0xe/0x10
[ +0.000002] task_work_run+0x9d/0xc0
[ +0.000002] exit_to_usermode_loop+0xc0/0xd0
[ +0.000001] do_syscall_64+0x115/0x130
[ +0.000002] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ +0.000002] RIP: 0033:0x7f64c37068d4
[ +0.000001] RSP: 002b:00007ffeaad50378 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[ +0.000001] RAX: 0000000000000000 RBX: 000055de952eaea0 RCX: 00007f64c37068d4
[ +0.000001] RDX: 000000000000000c RSI: 000055de952eaea0 RDI: 000000000000000c
[ +0.000001] RBP: 00007ffeaad503a0 R08: 000055de952e4598 R09: 0000000000000008
[ +0.000000] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffeaad50398
[ +0.000001] R13: 00007ffeaad504e0 R14: 00007ffeaad50550 R15: 000055de952e2ee0