[syzbot] [overlayfs?] WARNING in fast_dput

syzbot
2025-11-29T13:05:24Z

Hello,

syzbot found the following issue on:

HEAD commit: 7d31f578f323 Add linux-next specific files for 20251128
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14db5f42580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6336d8e94a7c517d
dashboard link: https://syzkaller.appspot.com/bug?extid=b74150fd2ef40e716ca2
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=1780a112580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10f6be92580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6b49d8ad90de/disk-7d31f578.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dbe2d4988ca7/vmlinux-7d31f578.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc0448ab2411/bzImage-7d31f578.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b74150fd2ef40e716ca2@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: fs/dcache.c:829 at fast_dput+0x334/0x430 fs/dcache.c:829, CPU#1: syz.0.17/6053
Modules linked in:
CPU: 1 UID: 0 PID: 6053 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:fast_dput+0x334/0x430 fs/dcache.c:829
Code: e3 81 ff 48 b8 00 00 00 00 00 fc ff df 41 0f b6 44 05 00 84 c0 0f 85 e2 00 00 00 41 80 0e 40 e9 fd fe ff ff e8 4d e3 81 ff 90 <0f> 0b 90 e9 ef fe ff ff 44 89 e6 81 e6 00 00 04 00 31 ff e8 74 e7
RSP: 0018:ffffc90003407cd8 EFLAGS: 00010293
RAX: ffffffff823fcfe3 RBX: ffff88806c44ac78 RCX: ffff88802e41bd00
RDX: 0000000000000000 RSI: 00000000ffffff80 RDI: 0000000000000001
RBP: 00000000ffffff80 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000680f8c R12: dffffc0000000000
R13: 1ffff1100d889597 R14: ffff88806c44abc0 R15: ffff88806c44acb8
FS: 00005555820e4500(0000) GS:ffff888125f4f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31b63fff CR3: 0000000072c78000 CR4: 00000000003526f0
Call Trace:
<TASK>
dput+0xe8/0x1a0 fs/dcache.c:924
__fput+0x68e/0xa70 fs/file_table.c:476
task_work_run+0x1d4/0x260 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
exit_to_user_mode_loop+0xff/0x4f0 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x2e3/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4966f8f749
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:00007ffc01c51258 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 000000000001a7a1 RCX: 00007f4966f8f749
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000201c5154f
R10: 0000001b30f20000 R11: 0000000000000246 R12: 00007f49671e5fac
R13: 00007f49671e5fa0 R14: ffffffffffffffff R15: 0000000000000004
</TASK>

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