Comment 4 for bug 1642767

I reproduced it with the latest mainline kernel as well:

Linux xenialbox 4.9.0-040900rc6-generic #201611201731 SMP Sun Nov 20 22:33:21 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Here's the slightly different syslog output:

Nov 22 14:36:55 xenialbox kernel: [ 484.506570] INFO: task systemd:3086 blocked for more than 120 seconds.
Nov 22 14:36:55 xenialbox kernel: [ 484.506578] Not tainted 4.9.0-040900rc6-generic #201611201731
Nov 22 14:36:55 xenialbox kernel: [ 484.506579] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Nov 22 14:36:55 xenialbox kernel: [ 484.506582] systemd D 0 3086 3076 0x00000104
Nov 22 14:36:55 xenialbox kernel: [ 484.506589] ffff8eaa1810bc00 ffff8eaa58f4d800 ffff8eaa57f59d00 ffff8eaa5fc19340
Nov 22 14:36:55 xenialbox kernel: [ 484.506593] ffff8eaa54bec880 ffff9bab80f17b78 ffffffff8bc87183 ffffffff8c244480
Nov 22 14:36:55 xenialbox kernel: [ 484.506596] 00ff8eaa57f59d00 ffff8eaa5fc19340 0000000000000000 ffff8eaa57f59d00
Nov 22 14:36:55 xenialbox kernel: [ 484.506600] Call Trace:
Nov 22 14:36:55 xenialbox kernel: [ 484.506622] [<ffffffff8bc87183>] ? __schedule+0x233/0x6e0
Nov 22 14:36:55 xenialbox kernel: [ 484.506626] [<ffffffff8bc87666>] schedule+0x36/0x80
Nov 22 14:36:55 xenialbox kernel: [ 484.506629] [<ffffffff8bc8a4da>] rwsem_down_write_failed+0x20a/0x380
Nov 22 14:36:55 xenialbox kernel: [ 484.506634] [<ffffffff8b463f3e>] ? kvm_sched_clock_read+0x1e/0x30
Nov 22 14:36:55 xenialbox kernel: [ 484.506643] [<ffffffff8b6ba5e0>] ? kernfs_sop_show_options+0x40/0x40
Nov 22 14:36:55 xenialbox kernel: [ 484.506651] [<ffffffff8b8265a7>] call_rwsem_down_write_failed+0x17/0x30
Nov 22 14:36:55 xenialbox kernel: [ 484.506655] [<ffffffff8bc89b1d>] down_write+0x2d/0x40
Nov 22 14:36:55 xenialbox kernel: [ 484.506658] [<ffffffff8b639fa0>] grab_super+0x30/0xa0
Nov 22 14:36:55 xenialbox kernel: [ 484.506661] [<ffffffff8b63a58f>] sget_userns+0x18f/0x4d0
Nov 22 14:36:55 xenialbox kernel: [ 484.506663] [<ffffffff8b6ba670>] ? kernfs_sop_show_path+0x50/0x50
Nov 22 14:36:55 xenialbox kernel: [ 484.506666] [<ffffffff8b6ba89e>] kernfs_mount_ns+0x7e/0x230
Nov 22 14:36:55 xenialbox kernel: [ 484.506674] [<ffffffff8b5230b8>] cgroup_mount+0x328/0x840
Nov 22 14:36:55 xenialbox kernel: [ 484.506679] [<ffffffff8b6036f5>] ? alloc_pages_current+0x95/0x140
Nov 22 14:36:55 xenialbox kernel: [ 484.506682] [<ffffffff8b63b578>] mount_fs+0x38/0x150
Nov 22 14:36:55 xenialbox kernel: [ 484.506686] [<ffffffff8b659177>] vfs_kern_mount+0x67/0x110
Nov 22 14:36:55 xenialbox kernel: [ 484.506688] [<ffffffff8b65baf1>] do_mount+0x1e1/0xcb0
Nov 22 14:36:55 xenialbox kernel: [ 484.506691] [<ffffffff8b6330df>] ? __check_object_size+0xff/0x1d6
Nov 22 14:36:55 xenialbox kernel: [ 484.506695] [<ffffffff8b60efe7>] ? kmem_cache_alloc_trace+0xd7/0x190
Nov 22 14:36:55 xenialbox kernel: [ 484.506697] [<ffffffff8b65c8d3>] SyS_mount+0x83/0xd0
Nov 22 14:36:55 xenialbox kernel: [ 484.506700] [<ffffffff8b403b6b>] do_syscall_64+0x5b/0xc0
Nov 22 14:36:55 xenialbox kernel: [ 484.506702] [<ffffffff8bc8c46f>] entry_SYSCALL64_slow_path+0x25/0x25