BUG: Dentry ffff8881e5655220{i=0,n=.index}  still in use (1) [unmount of ext4 loop2]
------------[ cut here ]------------
WARNING: CPU: 1 PID: 348 at fs/dcache.c:1597 umount_check+0x179/0x1c0 fs/dcache.c:1588
Modules linked in:
CPU: 1 PID: 348 Comm: syz-executor.2 Not tainted 5.4.125-syzkaller-00030-g1e429b8f9eb9 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:umount_check+0x179/0x1c0 fs/dcache.c:1588
Code: ff 4c 8b 0b 48 81 c5 20 04 00 00 48 c7 c7 a0 08 e9 84 4c 89 fe 4c 89 f2 4c 89 f9 45 89 e8 31 c0 55 e8 07 a2 af 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
RSP: 0018:ffff8881a6057c58 EFLAGS: 00010282
RAX: 0000000000000054 RBX: ffffffff85faa1c0 RCX: b04d5263cf7f9900
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: ffff8881e777b420 R08: ffffffff814e90e7 R09: ffffed103ede9608
R10: ffffed103ede9608 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881e5655220
FS:  00005555572ab400(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020cb9000 CR3: 00000001a678e000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 d_walk+0x2d9/0x540 fs/dcache.c:1307
 do_one_tree fs/dcache.c:1604 [inline]
 shrink_dcache_for_umount+0x8a/0x1a0 fs/dcache.c:1620
 generic_shutdown_super+0x63/0x2a0 fs/super.c:447
 kill_block_super+0x79/0xd0 fs/super.c:1444
 deactivate_locked_super+0xaf/0x100 fs/super.c:335
 deactivate_super+0x1b3/0x270 fs/super.c:366
 cleanup_mnt+0x432/0x4e0 fs/namespace.c:1102
 task_work_run+0x186/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:163 [inline]
 prepare_exit_to_usermode+0x2b0/0x310 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f7c2af97d37
Code: ff d0 48 89 c7 b8 3c 00 00 00 0f 05 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeaec126f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f7c2af97d37
RDX: 00007ffeaec127cb RSI: 0000000000000002 RDI: 00007ffeaec127c0
RBP: 00007ffeaec127c0 R08: 00000000ffffffff R09: 00007ffeaec12590
R10: 00005555572acbd3 R11: 0000000000000246 R12: 00007f7c2afefe80
R13: 00007ffeaec13880 R14: 00005555572acb00 R15: 00007ffeaec138c0
---[ end trace 9f79650d11d5ef73 ]---
BUG: Dentry ffff8881e5655220{i=0,n=.index}  still in use (1) [unmount of ext4 loop2]
------------[ cut here ]------------
WARNING: CPU: 1 PID: 348 at fs/dcache.c:1597 umount_check+0x179/0x1c0 fs/dcache.c:1588
Modules linked in:
CPU: 1 PID: 348 Comm: syz-executor.2 Tainted: G        W         5.4.125-syzkaller-00030-g1e429b8f9eb9 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:umount_check+0x179/0x1c0 fs/dcache.c:1588
Code: ff 4c 8b 0b 48 81 c5 20 04 00 00 48 c7 c7 a0 08 e9 84 4c 89 fe 4c 89 f2 4c 89 f9 45 89 e8 31 c0 55 e8 07 a2 af 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
RSP: 0018:ffff8881a6057c58 EFLAGS: 00010282
RAX: 0000000000000054 RBX: ffffffff85faa1c0 RCX: b04d5263cf7f9900
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000000
RBP: ffff8881e777b420 R08: ffffffff814e90e7 R09: ffffed103ede9608
R10: ffffed103ede9608 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881e5655220
FS:  00005555572ab400(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020cc6000 CR3: 00000001a678e000 CR4: 00000000003406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 d_walk+0x2d9/0x540 fs/dcache.c:1307
 do_one_tree fs/dcache.c:1604 [inline]
 shrink_dcache_for_umount+0x8a/0x1a0 fs/dcache.c:1620
 generic_shutdown_super+0x63/0x2a0 fs/super.c:447
 kill_block_super+0x79/0xd0 fs/super.c:1444
 deactivate_locked_super+0xaf/0x100 fs/super.c:335
 deactivate_super+0x1b3/0x270 fs/super.c:366
 cleanup_mnt+0x432/0x4e0 fs/namespace.c:1102
 task_work_run+0x186/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:163 [inline]
 prepare_exit_to_usermode+0x2b0/0x310 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f7c2af97d37
Code: ff d0 48 89 c7 b8 3c 00 00 00 0f 05 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeaec126f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f7c2af97d37
RDX: 00007ffeaec127cb RSI: 0000000000000002 RDI: 00007ffeaec127c0
RBP: 00007ffeaec127c0 R08: 00000000ffffffff R09: 00007ffeaec12590
R10: 00005555572acbd3 R11: 0000000000000246 R12: 00007f7c2afefe80
R13: 00007ffeaec13880 R14: 00005555572acb00 R15: 00007ffeaec138c0
---[ end trace 9f79650d11d5ef74 ]---
VFS: Busy inodes after unmount of loop2. Self-destruct in 5 seconds.  Have a nice day...