BUG: Dentry ADDR{i=0,n=/} still in use (-128) [unmount of erofs loop4]

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 13d2ce42 Linux 4.19.163
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10af845b500000
kernel config: https://syzkaller.appspot.com/x/.config?x=fac7c3360835a4e0
dashboard link: https://syzkaller.appspot.com/bug?extid=f357cf1216ab58cdc3fd
compiler: gcc (GCC) 10.1.0-syz 20200507

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+f357cf...@syzkaller.appspotmail.com

RAX: ffffffffffffffda RBX: 00007f373207cb10 RCX: 0000000000460b9a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f373207cad0
RBP: 00007f373207cad0 R08: 00007f373207cb10 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000020000000
R13: 0000000020000100 R14: 0000000020000200 R15: 0000000020000080
BUG: Dentry 000000000e3a4ef8{i=0,n=/} still in use (-128) [unmount of erofs loop4]
------------[ cut here ]------------
WARNING: CPU: 1 PID: 16303 at fs/dcache.c:1518 umount_check fs/dcache.c:1518 [inline]
WARNING: CPU: 1 PID: 16303 at fs/dcache.c:1518 umount_check.cold+0xf2/0x116 fs/dcache.c:1499
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 16303 Comm: syz-executor.4 Not tainted 4.19.163-syzkaller #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+0x1fc/0x2fe lib/dump_stack.c:118
panic+0x26a/0x50e kernel/panic.c:186
__warn.cold+0x20/0x61 kernel/panic.c:541
report_bug+0x262/0x2b0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
fixup_bug arch/x86/kernel/traps.c:173 [inline]
do_error_trap+0x1d7/0x310 arch/x86/kernel/traps.c:296
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1038
RIP: 0010:umount_check fs/dcache.c:1518 [inline]
RIP: 0010:umount_check.cold+0xf2/0x116 fs/dcache.c:1499
Code: ff 4d 89 f1 45 89 e0 48 89 e9 41 55 4c 89 fa 48 89 ee 48 c7 c7 c0 a2 74 88 e8 82 00 a4 ff 48 c7 c7 c0 a1 74 88 e8 76 00 a4 ff <0f> 0b 58 e9 fe 9a ff ff e8 9a 2f ef ff e9 22 ff ff ff 48 89 df e8
RSP: 0018:ffff888045d6fa98 EFLAGS: 00010286
RAX: 0000000000000024 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff814fdbb1 RDI: ffffed1008badf45
RBP: ffff88808e7fa5c0 R08: 0000000000000024 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000000 R12: 00000000ffffff80
R13: ffff888046420910 R14: ffffffff893f5040 R15: 0000000000000000
d_walk+0x196/0x990 fs/dcache.c:1253
do_one_tree fs/dcache.c:1525 [inline]
shrink_dcache_for_umount+0x87/0x330 fs/dcache.c:1541
generic_shutdown_super+0x68/0x370 fs/super.c:441
kill_block_super+0x97/0xf0 fs/super.c:1185
deactivate_locked_super+0x94/0x160 fs/super.c:329
mount_bdev+0x373/0x3b0 fs/super.c:1160
erofs_mount+0x8c/0xc0 drivers/staging/erofs/super.c:512
mount_fs+0xa3/0x30c fs/super.c:1261
vfs_kern_mount.part.0+0x68/0x470 fs/namespace.c:961
vfs_kern_mount fs/namespace.c:951 [inline]
do_new_mount fs/namespace.c:2469 [inline]
do_mount+0x113c/0x2f10 fs/namespace.c:2799
ksys_mount+0xcf/0x130 fs/namespace.c:3015
__do_sys_mount fs/namespace.c:3029 [inline]
__se_sys_mount fs/namespace.c:3026 [inline]
__x64_sys_mount+0xba/0x150 fs/namespace.c:3026
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x460b9a
Code: 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 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 8a 89 fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007f373207ca78 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f373207cb10 RCX: 0000000000460b9a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f373207cad0
RBP: 00007f373207cad0 R08: 00007f373207cb10 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000020000000
R13: 0000000020000100 R14: 0000000020000200 R15: 0000000020000080
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.