WARNING in filename_mknodat (2)

Status: moderation: reported on 2026/09/05 17:41
Subsystems: fs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+efaec66c5c0b57bbd651@syzkaller.appspotmail.com
First crash: 4d02h, last: 4d02h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
0ed359c5 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ WARNING in filename_mknodat (2) 2026/09/03 00:00 2026/09/03 00:00 2026/09/03 00:51 9941e97d
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in filename_mknodat prio:high fs -1 19 114d 200d 0/29 auto-obsoleted due to no activity on 2026/07/22 00:54

Sample crash report:
------------[ 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.1.18/5917
WARNING: kernel/locking/rtmutex_common.h:193 at rt_mutex_slowunlock+0x734/0xa30 kernel/locking/rtmutex.c:1432, CPU#0: syz.1.18/5917
Modules linked in:
CPU: 0 UID: 0 PID: 5917 Comm: syz.1.18 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 dc 5a 04 00 75 13 48 8d 3d 5c ce 5d 04 48 c7 c6 20 28 6d 8b <67> 48 0f b9 3a 90 e9 cf f9 ff ff 48 8d 3d 53 ce 5d 04 67 48 0f b9
RSP: 0018:ffffc9000647fce0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff888040b1b1a0 RCX: 0000000000080000
RDX: ffffc90011061000 RSI: ffffffff8b6d2820 RDI: ffffffff8fb4e0f0
RBP: ffffc9000647fdd0 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1f63dd9 R12: dffffc0000000000
R13: 1ffff92000c8ffa4 R14: ffff888040b1b150 R15: 0000000000000246
FS:  00007fd40cc356c0(0000) GS:ffff888125bd6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32b09ff8 CR3: 000000002c6bc000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 inode_unlock include/linux/fs.h:1034 [inline]
 end_dirop fs/namei.c:2955 [inline]
 end_creating include/linux/namei.h:120 [inline]
 end_creating_path fs/namei.c:5132 [inline]
 filename_mknodat+0x45c/0x670 fs/namei.c:5333
 __do_sys_mknod fs/namei.c:5356 [inline]
 __se_sys_mknod+0x3a/0x150 fs/namei.c:5353
 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: 0033:0x7fd40e9fe159
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:00007fd40cc35028 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007fd40ec86090 RCX: 00007fd40e9fe159
RDX: 0000000000000702 RSI: 0000000000008000 RDI: 0000200000000240
RBP: 00007fd40ea95024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd40ec86128 R14: 00007fd40ec86090 R15: 00007fff373123c8
 </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 dc 5a 04 00 	cmpl   $0x0,0x45adc39(%rip)        # 0x45adc53
  1a:	75 13                	jne    0x2f
  1c:	48 8d 3d 5c ce 5d 04 	lea    0x45dce5c(%rip),%rdi        # 0x45dce7f
  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 ce 5d 04 	lea    0x45dce53(%rip),%rdi        # 0x45dce8f
  3c:	67                   	addr32
  3d:	48                   	rex.W
  3e:	0f                   	.byte 0xf
  3f:	b9                   	.byte 0xb9

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/01 17:34 upstream 786262be6048 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs WARNING in filename_mknodat
* Struck through repros no longer work on HEAD.