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

[syzbot <syzbot+2a13ad6914e6fcec716c@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    654ae5d73c05 Merge tag 'drm-fixes-2026-09-05' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=143968f9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b454dc6b1b7acd30
dashboard link: https://syzkaller.appspot.com/bug?extid=2a13ad6914e6fcec716c
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/49c1a99f815b/disk-654ae5d7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6fcecf1b8c8d/vmlinux-654ae5d7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fa54b23691ca/bzImage-654ae5d7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2a13ad6914e6fcec716c@syzkaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current)
WARNING: kernel/locking/rtmutex_common.h:193 at debug_rt_mutex_unlock kernel/locking/rtmutex_common.h:193 [inline], CPU#0: syz.5.471/9806
WARNING: kernel/locking/rtmutex_common.h:193 at rt_mutex_slowunlock+0x734/0xa30 kernel/locking/rtmutex.c:1432, CPU#0: syz.5.471/9806
Modules linked in:
CPU: 0 UID: 0 PID: 9806 Comm: syz.5.471 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:debug_rt_mutex_unlock kernel/locking/rtmutex_common.h:193 [inline]
RIP: 0010:rt_mutex_slowunlock+0x73b/0xa30 kernel/locking/rtmutex.c:1432
Code: b1 8f 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 cf 02 00 00 83 3d 39 5d 5a 04 00 75 13 48 8d 3d 5c 4f 5d 04 48 c7 c6 20 28 6d 8b <67> 48 0f b9 3a 90 e9 cf f9 ff ff 48 8d 3d 53 4f 5d 04 67 48 0f b9
RSP: 0018:ffffc9000620fbc0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff888061d9a9f8 RCX: 0000000000080000
RDX: ffffc9000ddd9000 RSI: ffffffff8b6d2820 RDI: ffffffff8fb4e1f0
RBP: ffffc9000620fcb0 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1f63df9 R12: dffffc0000000000
R13: 1ffff92000c41f80 R14: ffff888061d9a9a8 R15: 0000000000000246
FS:  00007fc0841446c0(0000) GS:ffff888125bd4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd88506f52 CR3: 000000003a478000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 inode_unlock include/linux/fs.h:1034 [inline]
 __unlock_mount fs/namespace.c:2808 [inline]
 unlock_mount fs/namespace.c:2818 [inline]
 do_new_mount_fc fs/namespace.c:3795 [inline]
 do_new_mount+0x82d/0xdc0 fs/namespace.c:3848
 do_mount fs/namespace.c:4181 [inline]
 __do_sys_mount fs/namespace.c:4397 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4374
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc085f2e159
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:00007fc084144028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fc0861b6180 RCX: 00007fc085f2e159
RDX: 0000200000000080 RSI: 0000200000000040 RDI: 0000000000000000
RBP: 00007fc085fc5024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc0861b6218 R14: 00007fc0861b6180 R15: 00007ffc1374c1d8
 </TASK>
----------------
Code disassembly (best guess):
   0:	b1 8f                	mov    $0x8f,%cl
   2:	48 c1 e8 03          	shr    $0x3,%rax
   6:	42 0f b6 04 20       	movzbl (%rax,%r12,1),%eax
   b:	84 c0                	test   %al,%al
   d:	0f 85 cf 02 00 00    	jne    0x2e2
  13:	83 3d 39 5d 5a 04 00 	cmpl   $0x0,0x45a5d39(%rip)        # 0x45a5d53
  1a:	75 13                	jne    0x2f
  1c:	48 8d 3d 5c 4f 5d 04 	lea    0x45d4f5c(%rip),%rdi        # 0x45d4f7f
  23:	48 c7 c6 20 28 6d 8b 	mov    $0xffffffff8b6d2820,%rsi
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	90                   	nop
  30:	e9 cf f9 ff ff       	jmp    0xfffffa04
  35:	48 8d 3d 53 4f 5d 04 	lea    0x45d4f53(%rip),%rdi        # 0x45d4f8f
  3c:	67                   	addr32
  3d:	48                   	rex.W
  3e:	0f                   	.byte 0xf
  3f:	b9                   	.byte 0xb9


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