Re: [syzbot] [nilfs?] WARNING in nilfs_rename (2)

[Ryusuke Konishi <konishi.ryusuke@gmail.com>]

On Mon, Oct 13, 2025 at 6:23 PM syzbot
<syzbot+f6c7e1f1809f235eeb90@syzkaller.appspotmail.com> wrote:
>
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit:    2b763d465239 Add linux-next specific files for 20251010
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15847304580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=99cb6b007a8889ef
> dashboard link: https://syzkaller.appspot.com/bug?extid=f6c7e1f1809f235eeb90
> 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=1191867c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13847304580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6a00344625c3/disk-2b763d46.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/cd34c500f8eb/vmlinux-2b763d46.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/660905c62cb2/bzImage-2b763d46.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/25cb8f01270c/mount_0.gz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f6c7e1f1809f235eeb90@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> WARNING: fs/inode.c:417 at drop_nlink+0xc5/0x110 fs/inode.c:417, CPU#0: syz.0.217/6748
> Modules linked in:
> CPU: 0 UID: 0 PID: 6748 Comm: syz.0.217 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
> RIP: 0010:drop_nlink+0xc5/0x110 fs/inode.c:417
> Code: 70 07 00 00 be 08 00 00 00 e8 07 da e7 ff f0 48 ff 83 70 07 00 00 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc e8 dc 26 82 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:ffffc9000c52f9d0 EFLAGS: 00010293
> RAX: ffffffff823e1d34 RBX: ffff88805699e008 RCX: ffff888027213c80
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: ffffffff8f9e1877 R09: 1ffffffff1f3c30e
> R10: dffffc0000000000 R11: fffffbfff1f3c30f R12: 1ffff1100ad33c0a
> R13: ffff88805699d368 R14: ffff88805699e050 R15: dffffc0000000000
> FS:  00007f06f15f66c0(0000) GS:ffff888125d0b000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa97ff3f000 CR3: 0000000072f60000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  nilfs_rename+0x46a/0x820 fs/nilfs2/namei.c:418
>  vfs_rename+0xb34/0xe80 fs/namei.c:5216
>  do_renameat2+0x6a2/0xa50 fs/namei.c:5364
>  __do_sys_rename fs/namei.c:5411 [inline]
>  __se_sys_rename fs/namei.c:5409 [inline]
>  __x64_sys_rename+0x82/0x90 fs/namei.c:5409
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f06f078eec9
> 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:00007f06f15f6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
> RAX: ffffffffffffffda RBX: 00007f06f09e5fa0 RCX: 00007f06f078eec9
> RDX: 0000000000000000 RSI: 0000200000000180 RDI: 0000200000000040
> RBP: 00007f06f0811f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f06f09e6038 R14: 00007f06f09e5fa0 R15: 00007fffd3cbc518
>  </TASK>
>
>
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.

I have confirmed that this issue can be reproduced in 6.18-rc1 with
the reproducer.
It is not 100% reproducible, but I was able to reproduce it by
enabling the panic_on_warn option and continuing to run the program
for a while, so at this point I suspect that it is due to some kind of
underlying timing issue.

Ryusuke Konishi