[syzbot] [fuse?] WARNING in super_dev_register

[syzbot <syzbot+72fe3ea5814121fbc76e@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    6eb8711ece2c Add linux-next specific files for 20260702
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=144d2c0a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bc069df559a09463
dashboard link: https://syzkaller.appspot.com/bug?extid=72fe3ea5814121fbc76e
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11e32a6e580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10ebaf41580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ec0095ca90c5/disk-6eb8711e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e30096d3498c/vmlinux-6eb8711e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9855bbfe6176/bzImage-6eb8711e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+72fe3ea5814121fbc76e@syzkaller.appspotmail.com

         and is ignored by this kernel. Remove the mand
         option from the mount to silence this warning.
=======================================================
------------[ cut here ]------------
!sb->s_dev
WARNING: fs/super.c:509 at super_dev_register+0xf8/0x250 fs/super.c:509, CPU#1: syz.0.17/5906
Modules linked in:
CPU: 1 UID: 0 PID: 5906 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:super_dev_register+0xf8/0x250 fs/super.c:509
Code: 04 38 84 c0 0f 85 34 01 00 00 8b 2b 31 ff 89 ee e8 9d 2a 85 ff 85 ed 0f 85 98 00 00 00 e8 e0 25 85 ff eb 17 e8 d9 25 85 ff 90 <0f> 0b 90 48 85 db 75 c4 e8 cb 25 85 ff 90 0f 0b 90 43 0f b6 04 3c
RSP: 0018:ffffc90003f3f9d0 EFLAGS: 00010293
RAX: ffffffff82401307 RBX: ffff888032be2000 RCX: ffff88802d478000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff82401d10 R12: 1ffff11007997402
R13: dffffc0000000000 R14: ffff88803ccba010 R15: dffffc0000000000
FS:  0000555563c9e500(0000) GS:ffff888125b00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000003000 CR3: 00000000505ae000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 sget_fc+0x12f6/0x1a60 fs/super.c:896
 sget_dev fs/super.c:1480 [inline]
 get_tree_bdev_flags+0x212/0x4f0 fs/super.c:1867
 fuse_get_tree+0x194/0x3b0 fs/fuse/inode.c:1877
 vfs_get_tree+0x92/0x2a0 fs/super.c:1941
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3777 [inline]
 do_new_mount+0x319/0xdc0 fs/namespace.c:3853
 do_mount fs/namespace.c:4186 [inline]
 __do_sys_mount fs/namespace.c:4402 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4379
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2ea523de59
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:00007ffebb4997a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f2ea54c5fa0 RCX: 00007f2ea523de59
RDX: 0000200000000080 RSI: 00002000000000c0 RDI: 00002000000001c0
RBP: 00007f2ea52d3e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2ea54c5fac R14: 00007f2ea54c5fa0 R15: 00007f2ea54c5fa0
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup