Re: [syzbot] [gfs2?] WARNING in filename_mkdirat

[Christian Brauner]

On Mon, Feb 16, 2026 at 04:30:27PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    0f2acd3148e0 Merge tag 'm68knommu-for-v7.0' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15331c02580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ac00553de86d6bf0
> dashboard link: https://syzkaller.appspot.com/bug?extid=0ea5108a1f5fb4fcc2d8
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=146b295a580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-0f2acd31.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b7d134e71e9c/vmlinux-0f2acd31.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/b18643058ceb/bzImage-0f2acd31.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/bbfed09077d3/mount_1.gz
>   fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=106b295a580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+0ea5108a1f5fb4fcc2d8@xxxxxxxxxxxxxxxxxxxxxxxxx

Neil, is this something you have time to look into?

> 
> ------------[ cut here ]------------
> DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)): count = 0x0, magic = 0xffff88804a18c9b8, owner = 0x0, curr 0xffff888000ec2480, list empty
> WARNING: kernel/locking/rwsem.c:1381 at __up_write kernel/locking/rwsem.c:1380 [inline], CPU#0: syz.0.53/5774
> WARNING: kernel/locking/rwsem.c:1381 at up_write+0x2d6/0x410 kernel/locking/rwsem.c:1643, CPU#0: syz.0.53/5774
> Modules linked in:
> CPU: 0 UID: 0 PID: 5774 Comm: syz.0.53 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:__up_write kernel/locking/rwsem.c:1380 [inline]
> RIP: 0010:up_write+0x388/0x410 kernel/locking/rwsem.c:1643
> Code: cc 8b 49 c7 c2 c0 eb cc 8b 4c 0f 44 d0 48 8b 7c 24 08 48 c7 c6 20 ee cc 8b 48 8b 14 24 4c 89 f1 4d 89 e0 4c 8b 4c 24 10 41 52 <67> 48 0f b9 3a 48 83 c4 08 e8 ea 60 0a 03 e9 67 fd ff ff 48 c7 c1
> RSP: 0000:ffffc90006407d80 EFLAGS: 00010246
> RAX: ffffffff8bcceba0 RBX: ffff88804a18c9b8 RCX: ffff88804a18c9b8
> RDX: 0000000000000000 RSI: ffffffff8bccee20 RDI: ffffffff9014bf50
> RBP: ffff88804a18ca10 R08: 0000000000000000 R09: ffff888000ec2480
> R10: ffffffff8bcceba0 R11: ffffed1009431939 R12: 0000000000000000
> R13: dffffc0000000000 R14: ffff88804a18c9b8 R15: 1ffff11009431938
> FS:  00007f9e11bfe6c0(0000) GS:ffff88808ca62000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000c000d54e20 CR3: 0000000041f2c000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  inode_unlock include/linux/fs.h:1038 [inline]
>  end_dirop fs/namei.c:2947 [inline]
>  end_creating include/linux/namei.h:126 [inline]
>  end_creating_path fs/namei.c:4962 [inline]
>  filename_mkdirat+0x305/0x510 fs/namei.c:5271
>  __do_sys_mkdirat fs/namei.c:5287 [inline]
>  __se_sys_mkdirat+0x35/0x150 fs/namei.c:5284
>  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: 0033:0x7f9e10d9bf79
> 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:00007f9e11bfe028 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
> RAX: ffffffffffffffda RBX: 00007f9e11016090 RCX: 00007f9e10d9bf79
> RDX: 00000000000001c0 RSI: 0000200000000140 RDI: ffffffffffffff9c
> RBP: 00007f9e10e327e0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f9e11016128 R14: 00007f9e11016090 R15: 00007ffffd54f8b8
>  </TASK>
> ----------------
> Code disassembly (best guess), 2 bytes skipped:
>    0:	49 c7 c2 c0 eb cc 8b 	mov    $0xffffffff8bccebc0,%r10
>    7:	4c 0f 44 d0          	cmove  %rax,%r10
>    b:	48 8b 7c 24 08       	mov    0x8(%rsp),%rdi
>   10:	48 c7 c6 20 ee cc 8b 	mov    $0xffffffff8bccee20,%rsi
>   17:	48 8b 14 24          	mov    (%rsp),%rdx
>   1b:	4c 89 f1             	mov    %r14,%rcx
>   1e:	4d 89 e0             	mov    %r12,%r8
>   21:	4c 8b 4c 24 10       	mov    0x10(%rsp),%r9
>   26:	41 52                	push   %r10
> * 28:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
>   2d:	48 83 c4 08          	add    $0x8,%rsp
>   31:	e8 ea 60 0a 03       	call   0x30a6120
>   36:	e9 67 fd ff ff       	jmp    0xfffffda2
>   3b:	48                   	rex.W
>   3c:	c7                   	.byte 0xc7
>   3d:	c1                   	.byte 0xc1
> 
> 
> ---
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