[v6.6] BUG: Dentry still in use in unmount

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e617101e5626 Linux 6.6.110
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=110a4a14580000
kernel config: https://syzkaller.appspot.com/x/.config?x=12606d4b8832c7e4
dashboard link: https://syzkaller.appspot.com/bug?extid=5ce2c2133ed448b7bb4f
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9d9547c7a883/disk-e617101e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/69e0c4ff37a0/vmlinux-e617101e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d4ac8b3d2e09/bzImage-e617101e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5ce2c2...@syzkaller.appspotmail.com

gfs2: fsid=syz:syz.0: found 1 quota changes
------------[ cut here ]------------
BUG: Dentry ffff88805ef93608{i=925,n=/} still in use (5) [unmount of gfs2 loop2]
WARNING: CPU: 0 PID: 6417 at fs/dcache.c:1680 umount_check+0x186/0x1d0 fs/dcache.c:1672
Modules linked in:
CPU: 0 PID: 6417 Comm: syz.2.132 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:umount_check+0x186/0x1d0 fs/dcache.c:1672
Code: ea ff 4d 8b 0f 49 81 c5 60 06 00 00 48 c7 c7 c0 cc b7 8a 48 89 de 4c 89 f2 48 89 d9 41 89 e8 41 55 e8 ae 99 5d ff 48 83 c4 08 <0f> 0b 31 c0 5b 41 5c 41 5d 41 5e 41 5f 5d c3 89 f9 80 e1 07 80 c1
RSP: 0018:ffffc900040378f8 EFLAGS: 00010282
RAX: 13b3ead57065b800 RBX: ffff88805ef93608 RCX: 0000000000080000
RDX: ffffc9000ceba000 RSI: 0000000000029772 RDI: 0000000000029773
RBP: 0000000000000005 R08: ffffc900040374e7 R09: 1ffff92000806e9c
R10: dffffc0000000000 R11: fffff52000806e9d R12: dffffc0000000000
R13: ffff8880234b8660 R14: 0000000000000925 R15: ffffffff8d2cb6c0
FS: 00007f55a57ce6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f16abd19440 CR3: 00000000260b1000 CR4: 00000000003506f0
Call Trace:
<TASK>
d_walk+0x4c/0x700 fs/dcache.c:1367
do_one_tree+0x35/0xe0 fs/dcache.c:1687
shrink_dcache_for_umount+0x69/0x110 fs/dcache.c:1703
generic_shutdown_super+0x67/0x2b0 fs/super.c:665
kill_block_super+0x44/0x90 fs/super.c:1660
deactivate_locked_super+0x97/0x100 fs/super.c:481
gfs2_thaw_super+0x179/0x1e0 fs/gfs2/super.c:833
do_vfs_ioctl+0x1232/0x1bb0 fs/ioctl.c:-1
__do_sys_ioctl fs/ioctl.c:869 [inline]
__se_sys_ioctl+0x83/0x170 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f55a498eec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f55a57ce038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f55a4be5fa0 RCX: 00007f55a498eec9
RDX: 0000000000000000 RSI: 00000000c0045878 RDI: 0000000000000004
RBP: 00007f55a4a11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f55a4be6038 R14: 00007f55a4be5fa0 R15: 00007ffe39cf75d8
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: e617101e5626 Linux 6.6.110
git tree: linux-6.6.y

console output: https://syzkaller.appspot.com/x/log.txt?x=1213e304580000

kernel config: https://syzkaller.appspot.com/x/.config?x=12606d4b8832c7e4
dashboard link: https://syzkaller.appspot.com/bug?extid=5ce2c2133ed448b7bb4f
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1189852f980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=131e3458580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5e096b5ec298/disk-e617101e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/074307bb1464/vmlinux-e617101e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/68e0d6ffb47c/bzImage-e617101e.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/f0c759d6de5e/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=12811892580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5ce2c2...@syzkaller.appspotmail.com

gfs2: fsid=syz:syz.0: first mount done, others may mount
------------[ cut here ]------------
BUG: Dentry ffff88806144f490{i=925,n=/} still in use (3) [unmount of gfs2 loop0]
WARNING: CPU: 0 PID: 5950 at fs/dcache.c:1680 umount_check+0x186/0x1d0 fs/dcache.c:1672
Modules linked in:
CPU: 0 PID: 5950 Comm: syz.0.17 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:umount_check+0x186/0x1d0 fs/dcache.c:1672
Code: ea ff 4d 8b 0f 49 81 c5 60 06 00 00 48 c7 c7 c0 cc b7 8a 48 89 de 4c 89 f2 48 89 d9 41 89 e8 41 55 e8 ae 99 5d ff 48 83 c4 08 <0f> 0b 31 c0 5b 41 5c 41 5d 41 5e 41 5f 5d c3 89 f9 80 e1 07 80 c1

RSP: 0018:ffffc900033178f8 EFLAGS: 00010282
RAX: be92a052eaecb500 RBX: ffff88806144f490 RCX: ffff888026045a00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 0000000000000003 R08: ffffc900033174e7 R09: 1ffff92000662e9c
R10: dffffc0000000000 R11: fffff52000662e9d R12: dffffc0000000000
R13: ffff88807b352660 R14: 0000000000000925 R15: ffffffff8d2cb6c0
FS: 0000555582221500(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000001b2d963fff CR3: 0000000076491000 CR4: 00000000003506f0

Call Trace:
<TASK>
d_walk+0x4c/0x700 fs/dcache.c:1367
do_one_tree+0x35/0xe0 fs/dcache.c:1687
shrink_dcache_for_umount+0x69/0x110 fs/dcache.c:1703
generic_shutdown_super+0x67/0x2b0 fs/super.c:665
kill_block_super+0x44/0x90 fs/super.c:1660
deactivate_locked_super+0x97/0x100 fs/super.c:481
gfs2_thaw_super+0x179/0x1e0 fs/gfs2/super.c:833
do_vfs_ioctl+0x1232/0x1bb0 fs/ioctl.c:-1
__do_sys_ioctl fs/ioctl.c:869 [inline]
__se_sys_ioctl+0x83/0x170 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

RIP: 0033:0x7fab4878eec9

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007fffe13511d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fab489e5fa0 RCX: 00007fab4878eec9
RDX: 0000000000000000 RSI: 00000000c0045878 RDI: 0000000000000003
RBP: 00007fab48811f91 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007fab489e5fa0 R14: 00007fab489e5fa0 R15: 0000000000000002
</TASK>


---
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