BUG: Dentry still in use [unmount of ext4 loop1]

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cd5f5cb9 ANDROID: GKI: Export memblock_free to drivers
git tree: android12-5.4
console output: https://syzkaller.appspot.com/x/log.txt?x=159ef137500000
kernel config: https://syzkaller.appspot.com/x/.config?x=17c7bb5b502bc58a
dashboard link: https://syzkaller.appspot.com/bug?extid=ab5b9d7a8be90397edba
compiler: Android (6032204 based on r370808) clang version 10.0.1 (https://android.googlesource.com/toolchain/llvm-project 6e765c10313d15c02ab29977a82938f66742c3a9)

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ab5b9d...@syzkaller.appspotmail.com

BUG: Dentry 00000000ab22b1f9{i=0,n=.index} still in use (1) [unmount of ext4 loop1]
------------[ cut here ]------------
WARNING: CPU: 0 PID: 379 at fs/dcache.c:1597 umount_check+0x179/0x1c0 fs/dcache.c:1588
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 379 Comm: syz-executor.1 Not tainted 5.4.84-syzkaller-00151-gcd5f5cb9fe67 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1dd/0x24e lib/dump_stack.c:118
panic+0x285/0x750 kernel/panic.c:221
__warn+0x1fd/0x200 kernel/panic.c:582
report_bug+0x390/0x4d0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:179 [inline]
do_error_trap arch/x86/kernel/traps.c:272 [inline]
do_invalid_op+0x6e/0x110 arch/x86/kernel/traps.c:291
invalid_op+0x1e/0x30 arch/x86/entry/entry_64.S:1029
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 e3 3d 1d 85 4c 89 fe 4c 89 f2 4c 89 f9 45 89 e8 31 c0 55 e8 27 54 b0 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:ffff8881a8907c60 EFLAGS: 00010296
RAX: 0000000000000054 RBX: ffffffff8548a3b8 RCX: 6445d59ff8091c00
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: ffff88819838d420 R08: ffffffff814e3401 R09: ffffed103ee05e08
R10: ffffed103ee05e08 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881a2a55bb0
d_walk+0x2e9/0x570 fs/dcache.c:1307
do_one_tree fs/dcache.c:1604 [inline]
shrink_dcache_for_umount+0x8a/0x1b0 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+0x1b8/0x280 fs/super.c:366
cleanup_mnt+0x432/0x4e0 fs/namespace.c:1102
task_work_run+0x176/0x1a0 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: 0033:0x460b77
Code: 64 89 04 25 d0 02 00 00 58 5f ff d0 48 89 c7 e8 2f be ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 ad 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff1b1301c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000460b77
RDX: 00000000004032c8 RSI: 0000000000000002 RDI: 00007fff1b130270
RBP: 000000000000006b R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000005 R11: 0000000000000246 R12: 00007fff1b131300
R13: 0000000003236940 R14: 0000000000000000 R15: 000000000002942b
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.