BUG: Dentry still in use [unmount of sysfs sysfs]

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc044639 UPSTREAM: mm/ksm: Remove reuse_ksm_page()
git tree: android12-5.4
console output: https://syzkaller.appspot.com/x/log.txt?x=12cc2984d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=63043a451b4568fd
dashboard link: https://syzkaller.appspot.com/bug?extid=f281dee6f8bb07dba42a
compiler: Android (6032204 based on r370808) clang version 10.0.1 (https://android.googlesource.com/toolchain/llvm-project 6e765c10313d15c02ab29977a82938f66742c3a9)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12f72900d00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=179e3a3b500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f281de...@syzkaller.appspotmail.com

incfs: Can't find or create .index dir in ./file0
BUG: Dentry 0000000027ff9616{i=0,n=.index} still in use (1) [unmount of sysfs sysfs]
------------[ cut here ]------------
WARNING: CPU: 0 PID: 359 at fs/dcache.c:1597 umount_check+0x179/0x1c0 fs/dcache.c:1588
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 359 Comm: syz-executor629 Not tainted 5.4.89-syzkaller-00264-gdc04463953b2 #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 c3 53 1d 85 4c 89 fe 4c 89 f2 4c 89 f9 45 89 e8 31 c0 55 e8 47 42 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:ffff8881e8cf7a00 EFLAGS: 00010296
RAX: 0000000000000055 RBX: ffffffff8547f4d8 RCX: fa1a1a8c0b467300
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
RBP: ffff8881e8b18420 R08: ffffffff814e4601 R09: ffffed103ee05e08
R10: ffffed103ee05e08 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881efec6660
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_anon_super+0x36/0x60 fs/super.c:1108
kernfs_kill_sb+0x120/0x140 fs/kernfs/mount.c:360
sysfs_kill_sb+0x1e/0x30 fs/sysfs/mount.c:86
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
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0xcc2/0x2830 kernel/exit.c:811
do_group_exit+0x155/0x2b0 kernel/exit.c:909
__do_sys_exit_group+0x13/0x20 kernel/exit.c:920
__se_sys_exit_group+0x10/0x10 kernel/exit.c:918
__x64_sys_exit_group+0x37/0x40 kernel/exit.c:918
do_syscall_64+0xcb/0x150 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x43f758
Code: Bad RIP value.
RSP: 002b:00007ffebd7788e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 000000000043f758
RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
RBP: 00000000004bf710 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d1180 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.