TITLE: BUG: Dentry still in use in unmount
ALT: BUG: Dentry still in use [unmount of ramfs ramfs]

[   20.143962][  T367] BUG: Dentry ffff888119d8a000{i=0,n=.index}  still in use (1) [unmount of ramfs ramfs]
[   20.175803][  T367] ------------[ cut here ]------------
[   20.202650][  T367] WARNING: CPU: 0 PID: 367 at fs/dcache.c:1616 umount_check+0x18d/0x1d0
[   20.233554][  T367] Modules linked in:
[   20.329716][  T367] 
[   20.332025][  T367] CPU: 0 PID: 367 Comm: syz-executor388 Not tainted 5.10.75-syzkaller-01082-g234d53d2bb60 #0
[   20.342163][  T367] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[   20.352222][  T367] RIP: 0010:umount_check+0x18d/0x1d0
[   20.357505][  T367] Code: 8b 0b 49 81 c6 f8 03 00 00 48 c7 c7 00 40 2e 85 4c 89 e6 48 8b 55 d0 4c 89 e1 45 89 f8 31 c0 41 56 e8 ae d9 9e ff 48 83 c4 08 <0f> 0b e9 f1 fe ff ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c c9 fe ff
[   20.377112][  T367] RSP: 0018:ffffc9000096f770 EFLAGS: 00010292
[   20.383152][  T367] RAX: 0000000000000055 RBX: ffffffff866af200 RCX: 1ad6b89836e5b500
[   20.391121][  T367] RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
[   20.399088][  T367] RBP: ffffc9000096f7a0 R08: ffffffff81545368 R09: 0000000000000003
[   20.407058][  T367] R10: fffff5200012de41 R11: 0000000000000004 R12: ffff888119d8a000
[   20.415035][  T367] R13: dffffc0000000000 R14: ffff88811d7373f8 R15: 0000000000000001
[   20.422991][  T367] FS:  0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
[   20.431922][  T367] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   20.438500][  T367] CR2: 00007f01b7bddb68 CR3: 000000010c4f0000 CR4: 00000000003506b0
[   20.446472][  T367] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   20.454425][  T367] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   20.462392][  T367] Call Trace:
[   20.465694][  T367]  d_walk+0x309/0x540
[   20.473799][  T367]  shrink_dcache_for_umount+0x8e/0x1b0
[   20.479270][  T367]  generic_shutdown_super+0x66/0x2c0
[   20.484539][  T367]  kill_litter_super+0x75/0xa0
[   20.489305][  T367]  ramfs_kill_sb+0x44/0x50
[   20.493720][  T367]  deactivate_locked_super+0xb0/0x100
[   20.499135][  T367]  deactivate_super+0xa5/0xd0
[   20.503806][  T367]  cleanup_mnt+0x45f/0x510
[   20.508231][  T367]  __cleanup_mnt+0x19/0x20
[   20.512632][  T367]  task_work_run+0x147/0x1b0
[   20.517286][  T367]  do_exit+0x70e/0x23a0
[   20.550515][  T367]  do_group_exit+0x16a/0x2d0
[   20.555114][  T367]  get_signal+0x133e/0x1f80
[   20.588205][  T367]  arch_do_signal+0x8d/0x620
[   20.598246][  T367]  exit_to_user_mode_prepare+0xaa/0xe0
[   20.603696][  T367]  syscall_exit_to_user_mode+0x24/0x40
[   20.609159][  T367]  do_syscall_64+0x3d/0x70
[   20.613565][  T367]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   20.619472][  T367] RIP: 0033:0x7f01b7b884f9
[   20.623869][  T367] Code: Unable to access opcode bytes at RIP 0x7f01b7b884cf.
[   20.631232][  T367] RSP: 002b:00007f01b7b19308 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
[   20.639658][  T367] RAX: fffffffffffffe00 RBX: 00007f01b7c103f8 RCX: 00007f
