[moderation] [fs?] WARNING in do_new_mount (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c22e26bd0906 Merge tag 'landlock-7.0-rc1' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13924722580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6428d17febdfb14e
dashboard link: https://syzkaller.appspot.com/bug?extid=aa9301d3b66961eb2421
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d68a15a17667/disk-c22e26bd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b8799409c3a5/vmlinux-c22e26bd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2c41c867ca47/bzImage-c22e26bd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aa9301...@syzkaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current)
WARNING: kernel/locking/rtmutex_common.h:182 at debug_rt_mutex_unlock kernel/locking/rtmutex_common.h:182 [inline], CPU#1: syz.2.122/6750
WARNING: kernel/locking/rtmutex_common.h:182 at rt_mutex_slowunlock+0x6d9/0x8b0 kernel/locking/rtmutex.c:1419, CPU#1: syz.2.122/6750
Modules linked in:
CPU: 1 UID: 0 PID: 6750 Comm: syz.2.122 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:debug_rt_mutex_unlock kernel/locking/rtmutex_common.h:182 [inline]
RIP: 0010:rt_mutex_slowunlock+0x6e0/0x8b0 kernel/locking/rtmutex.c:1419
Code: 49 8f 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 c0 01 00 00 83 3d d4 37 35 04 00 75 13 48 8d 3d 47 3b 38 04 48 c7 c6 00 06 2d 8b <67> 48 0f b9 3a 90 e9 2a fa ff ff 90 0f 0b 90 e9 4c fe ff ff be 02
RSP: 0018:ffffc9000d7d7bc0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8880407de790 RCX: 0000000000080000
RDX: ffffc9000ebac000 RSI: ffffffff8b2d0600 RDI: ffffffff8f4c3e70
RBP: ffffc9000d7d7cb0 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1e9275f R12: dffffc0000000000
R13: 1ffff92001afaf80 R14: 0000000000000246 R15: ffff8880407de740
FS: 00007fab8b3f56c0(0000) GS:ffff888126695000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7ae5ce3d58 CR3: 0000000037fea000 CR4: 00000000003526f0
Call Trace:
<TASK>
inode_unlock include/linux/fs.h:1038 [inline]
__unlock_mount fs/namespace.c:2780 [inline]
unlock_mount fs/namespace.c:2790 [inline]
do_new_mount_fc fs/namespace.c:3783 [inline]
do_new_mount+0x7c6/0xd30 fs/namespace.c:3836
do_mount fs/namespace.c:4159 [inline]
__do_sys_mount fs/namespace.c:4348 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4325
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fab8d1bbf79
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fab8b3f5028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fab8d436090 RCX: 00007fab8d1bbf79
RDX: 0000200000000080 RSI: 0000200000000180 RDI: 0000000000000000
RBP: 00007fab8d2527e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000001214040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fab8d436128 R14: 00007fab8d436090 R15: 00007ffea7601358
</TASK>
----------------
Code disassembly (best guess), 2 bytes skipped:
0: 48 c1 e8 03 shr $0x3,%rax
4: 42 0f b6 04 20 movzbl (%rax,%r12,1),%eax
9: 84 c0 test %al,%al
b: 0f 85 c0 01 00 00 jne 0x1d1
11: 83 3d d4 37 35 04 00 cmpl $0x0,0x43537d4(%rip) # 0x43537ec
18: 75 13 jne 0x2d
1a: 48 8d 3d 47 3b 38 04 lea 0x4383b47(%rip),%rdi # 0x4383b68
21: 48 c7 c6 00 06 2d 8b mov $0xffffffff8b2d0600,%rsi
* 28: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2d: 90 nop
2e: e9 2a fa ff ff jmp 0xfffffa5d
33: 90 nop
34: 0f 0b ud2
36: 90 nop
37: e9 4c fe ff ff jmp 0xfffffe88
3c: be .byte 0xbe
3d: 02 .byte 0x2


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