OK
[    7.310950][  T134] rcS (134) used greatest stack depth: 26456 bytes left

syzkaller
syzkaller login: [   14.907464][   T22] kauditd_printk_skb: 60 callbacks suppressed
[   14.907471][   T22] audit: type=1400 audit(1635399683.159:71): avc:  denied  { transition } for  pid=266 comm="sshd" path="/bin/sh" dev="sda1" ino=73 scontext=system_u:system_r:initrc_t tcontext=root:sysadm_r:sysadm_t tclass=process permissive=1
[   14.913138][   T22] audit: type=1400 audit(1635399683.169:72): avc:  denied  { write } for  pid=266 comm="sh" path="pipe:[10513]" dev="pipefs" ino=10513 scontext=root:sysadm_r:sysadm_t tcontext=system_u:system_r:initrc_t tclass=fifo_file permissive=1
[   14.915922][  T266] sh (266) used greatest stack depth: 26280 bytes left
Warning: Permanently added '10.128.0.80' (ECDSA) to the list of known hosts.
executing program
[   22.267119][   T22] audit: type=1400 audit(1635399690.519:73): avc:  denied  { execmem } for  pid=299 comm="syz-executor374" scontext=root:sysadm_r:sysadm_t tcontext=root:sysadm_r:sysadm_t tclass=process permissive=1
[   22.288065][   T22] audit: type=1400 audit(1635399690.529:74): avc:  denied  { mounton } for  pid=301 comm="syz-executor374" path="/sys/fs/fuse/connections" dev="fusectl" ino=1 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:fusefs_t tclass=dir permissive=1
[   22.313463][   T22] audit: type=1400 audit(1635399690.529:75): avc:  denied  { mount } for  pid=301 comm="syz-executor374" name="/" dev="fusectl" ino=1 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:fusefs_t tclass=filesystem permissive=1
[   22.315986][  T301] EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue
[   22.335965][   T22] audit: type=1400 audit(1635399690.529:76): avc:  denied  { mounton } for  pid=301 comm="syz-executor374" path="/" dev="sda1" ino=2 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:root_t tclass=dir permissive=1
[   22.347730][  T301] EXT4-fs error (device loop0): __ext4_new_inode:929: comm syz-executor374: reserved inode found cleared - inode=1
[   22.366414][   T22] audit: type=1400 audit(1635399690.549:77): avc:  denied  { read write } for  pid=301 comm="syz-executor374" name="loop0" dev="devtmpfs" ino=9363 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:fixed_disk_device_t tclass=blk_file permissive=1
[   22.378457][  T301] incfs: Can't find or create .index dir in ./file0
[   22.402631][   T22] audit: type=1400 audit(1635399690.549:78): avc:  denied  { open } for  pid=301 comm="syz-executor374" path="/dev/loop0" dev="devtmpfs" ino=9363 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:fixed_disk_device_t tclass=blk_file permissive=1
[   22.433163][   T22] audit: type=1400 audit(1635399690.549:79): avc:  denied  { ioctl } for  pid=301 comm="syz-executor374" path="/dev/loop0" dev="devtmpfs" ino=9363 ioctlcmd=0x4c00 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:fixed_disk_device_t tclass=blk_file permissive=1
[   22.433292][  T301] BUG: Dentry ffff8881e6675220{i=0,n=.index}  still in use (1) [unmount of ext4 loop0]
[   22.458793][   T22] audit: type=1400 audit(1635399690.549:80): avc:  denied  { mounton } for  pid=301 comm="syz-executor374" path="/root/file0" dev="sda1" ino=1137 scontext=root:sysadm_r:sysadm_t tcontext=root:object_r:user_home_t tclass=dir permissive=1
[   22.468445][  T301] ------------[ cut here ]------------
[   22.491051][   T22] audit: type=1400 audit(1635399690.609:81): avc:  denied  { mount } for  pid=301 comm="syz-executor374" name="/" dev="loop0" ino=2 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:fs_t tclass=filesystem permissive=1
[   22.496477][  T301] WARNING: CPU: 1 PID: 301 at fs/dcache.c:1597 umount_check+0x179/0x1c0
[   22.518241][   T22] audit: type=1400 audit(1635399690.609:82): avc:  denied  { mounton } for  pid=301 comm="syz-executor374" path="/root/file0" dev="loop0" ino=2 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=dir permissive=1
[   22.526517][  T301] Modules linked in:
[   22.526529][  T301] CPU: 1 PID: 301 Comm: syz-executor374 Not tainted 5.4.147-syzkaller-00039-gcbb80ec0faf2 #0
[   22.526532][  T301] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[   22.526546][  T301] RIP: 0010:umount_check+0x179/0x1c0
[   22.578569][  T301] Code: ff 4c 8b 0b 48 81 c5 20 04 00 00 48 c7 c7 60 13 c9 84 4c 89 fe 4c 89 f2 4c 89 f9 45 89 e8 31 c0 55 e8 b7 0e b3 ff 48 83 c4 08 <0f> 0b e9 fd fe ff ff 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c d4 fe ff
[   22.598154][  T301] RSP: 0018:ffff8881de6d7b78 EFLAGS: 00010286
[   22.604187][  T301] RAX: 0000000000000054 RBX: ffffffff85daa5c0 RCX: c69cf0308631ce00
[   22.612144][  T301] RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
[   22.620085][  T301] RBP: ffff8881de0c1420 R08: ffffffff814b2a4c R09: ffffed103bcdaf27
[   22.628038][  T301] R10: ffffed103bcdaf27 R11: 0000000000000000 R12: dffffc0000000000
[   22.635994][  T301] R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881e6675220
[   22.643948][  T301] FS:  000055555713d300(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
[   22.652839][  T301] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   22.659388][  T301] CR2: 00007f979753b1d0 CR3: 00000001ed7e5000 CR4: 00000000003406e0
[   22.667337][  T301] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   22.675277][  T301] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   22.683224][  T301] Call Trace:
[   22.686488][  T301]  d_walk+0x2d9/0x540
[   22.690453][  T301]  ? __d_free+0x20/0x20
[   22.694584][  T301]  shrink_dcache_for_umount+0x8a/0x1a0
[   22.700020][  T301]  generic_shutdown_super+0x63/0x2a0
[   22.705274][  T301]  kill_block_super+0x79/0xd0
[   22.709921][  T301]  deactivate_locked_super+0xaf/0x100
[   22.715276][  T301]  deactivate_super+0x168/0x210
[   22.720093][  T301]  cleanup_mnt+0x432/0x4e0
[   22.724475][  T301]  task_work_run+0x186/0x1b0
[   22.729047][  T301]  do_exit+0xc0a/0x2aa0
[   22.733171][  T301]  do_group_exit+0x15c/0x2c0
[   22.737726][  T301]  ? do_user_addr_fault+0x6b0/0xb40
[   22.742889][  T301]  __do_sys_exit_group+0x13/0x20
[   22.747803][  T301]  __se_sys_exit_group+0x10/0x10
[   22.752708][  T301]  __x64_sys_exit_group+0x37/0x40
[   22.757699][  T301]  do_syscall_64+0xcb/0x1e0
[   22.762170][  T301]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   22.768031][  T301] RIP: 0033:0x7f97974c6019
[   22.772414][  T301] Code: Bad RIP value.
[   22.776446][  T301] RSP: 002b:00007ffed7a330c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
[   22.784836][  T301] RAX: ffffffffffffffda RBX: 00007f979753a330 RCX: 00007f97974c6019
[   22.792774][  T301] RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000001
[   22.800712][  T301] RBP: 0000000000000001 R08: ffffffffffffffc0 R09: 00007f9797534e40
[   22.808651][  T301] R10: 0000000000000011 R11: 0000000000000246 R12: 00007f979753a330
[   22.816593][  T301] R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
[   22.824546][  T301] ---[ end trace 1fc8806467dbc07b ]---
[   22.831466][  T301] VFS: Busy inodes after unmount of loop0. Self-destruct in 5 seconds.  Have a nice day...