[syzbot] [overlayfs?] WARNING in shmem_unlink

[syzbot <syzbot+ec9fab8b7f0386b98a17@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    0cc53520e68b Merge tag 'probes-fixes-v6.17-rc1' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14a003a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=13f39c6a0380a209
dashboard link: https://syzkaller.appspot.com/bug?extid=ec9fab8b7f0386b98a17
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1387bc34580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1f4865acb167/disk-0cc53520.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/14540c5ef981/vmlinux-0cc53520.xz
kernel image: https://storage.googleapis.com/syzbot-assets/35534bfe1c7e/bzImage-0cc53520.xz

Bisection is inconclusive: the first bad commit could be any of:

241062ae5d87 ovl: change ovl_workdir_cleanup() to take dir lock as needed.
a45ee87ded78 ovl: narrow locking in ovl_workdir_cleanup_recurse()
c69566b1d11d ovl: narrow locking on ovl_remove_and_whiteout()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=130d1dbc580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ec9fab8b7f0386b98a17@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 9026 at fs/inode.c:417 drop_nlink+0xc5/0x110 fs/inode.c:417
Modules linked in:
CPU: 1 UID: 0 PID: 9026 Comm: syz.4.1430 Tainted: G        W           6.17.0-rc1-syzkaller-00038-g0cc53520e68b #0 PREEMPT_{RT,(full)} 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:drop_nlink+0xc5/0x110 fs/inode.c:417
Code: c8 08 00 00 be 08 00 00 00 e8 b7 90 ec ff f0 48 ff 83 c8 08 00 00 5b 41 5c 41 5e 41 5f 5d e9 82 9f c8 08 cc e8 dc 5a 8d ff 90 <0f> 0b 90 eb 81 44 89 f1 80 e1 07 80 c1 03 38 c1 0f 8c 5b ff ff ff
RSP: 0018:ffffc9000f5ef600 EFLAGS: 00010293
RAX: ffffffff82310064 RBX: ffff88803352c420 RCX: ffff88802cfcbb80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52001ebdeb5 R12: 1ffff110066a588d
R13: 00000000689e7afa R14: ffff88803352c468 R15: dffffc0000000000
FS:  00007fec6bd366c0(0000) GS:ffff8881269c5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555591d73608 CR3: 00000000274f4000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 shmem_unlink+0x1f5/0x2d0 mm/shmem.c:4041
 vfs_unlink+0x39a/0x660 fs/namei.c:4586
 ovl_do_unlink fs/overlayfs/overlayfs.h:218 [inline]
 ovl_cleanup_locked fs/overlayfs/dir.c:36 [inline]
 ovl_cleanup+0x151/0x230 fs/overlayfs/dir.c:56
 ovl_check_rename_whiteout fs/overlayfs/super.c:607 [inline]
 ovl_make_workdir fs/overlayfs/super.c:704 [inline]
 ovl_get_workdir+0xabd/0x17c0 fs/overlayfs/super.c:827
 ovl_fill_super+0x1365/0x35b0 fs/overlayfs/super.c:1406
 vfs_get_super fs/super.c:1325 [inline]
 get_tree_nodev+0xbb/0x150 fs/super.c:1344
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
 do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
 do_mount fs/namespace.c:4133 [inline]
 __do_sys_mount fs/namespace.c:4344 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4321
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fec6c6cebe9
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:00007fec6bd36038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fec6c8f5fa0 RCX: 00007fec6c6cebe9
RDX: 0000200000000200 RSI: 0000200000000000 RDI: 0000000000000000
RBP: 00007fec6c751e19 R08: 0000200000000140 R09: 0000000000000000
R10: 00000000000000d4 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fec6c8f6038 R14: 00007fec6c8f5fa0 R15: 00007ffc15eea8d8
 </TASK>


---
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