[syzbot] [btrfs?] WARNING in create_reloc_root

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7404ce516372 Merge tag 's390-7.2-3' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=145075dc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=20c9876b0f77b546
dashboard link: https://syzkaller.appspot.com/bug?extid=aca623fc25065fa06615
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 (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-7404ce51.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3c0f4563b500/vmlinux-7404ce51.xz
kernel image: https://storage.googleapis.com/syzbot-assets/320dddfc3ad1/bzImage-7404ce51.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aca623...@syzkaller.appspotmail.com

FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 1
CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 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
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
fail_dump lib/fault-inject.c:73 [inline]
should_fail_ex+0x40c/0x560 lib/fault-inject.c:174
should_failslab+0xa8/0x100 mm/failslab.c:46
slab_pre_alloc_hook mm/slub.c:4567 [inline]
slab_alloc_node mm/slub.c:4925 [inline]
__kmalloc_cache_noprof+0xa8/0x660 mm/slub.c:5511
_kmalloc_noprof include/linux/slab.h:969 [inline]
__add_reloc_root+0x75/0x4e0 fs/btrfs/relocation.c:577
btrfs_init_reloc_root+0x3d6/0x590 fs/btrfs/relocation.c:800
record_root_in_trans+0x27c/0x330 fs/btrfs/transaction.c:462
btrfs_record_root_in_trans+0x15a/0x180 fs/btrfs/transaction.c:508
start_transaction+0x3a6/0x18b0 fs/btrfs/transaction.c:794
create_snapshot fs/btrfs/ioctl.c:795 [inline]
btrfs_mksubvol+0x8c6/0x10c0 fs/btrfs/ioctl.c:887
btrfs_mksnapshot+0xa3/0xe0 fs/btrfs/ioctl.c:929
__btrfs_ioctl_snap_create+0x45d/0x6b0 fs/btrfs/ioctl.c:1191
btrfs_ioctl_snap_create_v2+0x1e9/0x370 fs/btrfs/ioctl.c:1261
btrfs_ioctl+0x8eb/0xd50 fs/btrfs/ioctl.c:-1
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
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: 0033:0x7fc6fe59de59
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:00007fc6ff51bfe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc6fe826090 RCX: 00007fc6fe59de59
RDX: 0000200000002480 RSI: 0000000050009417 RDI: 0000000000000005
RBP: 00007fc6ff51c050 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007fc6fe826128 R14: 00007fc6fe826090 R15: 00007ffc03132988
</TASK>
------------[ cut here ]------------
btrfs_abort_should_print_stack(__error)
WARNING: fs/btrfs/relocation.c:735 at create_reloc_root+0x9d2/0xb80 fs/btrfs/relocation.c:735, CPU#0: syz.0.0/5321
Modules linked in:
CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 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:create_reloc_root+0x9d2/0xb80 fs/btrfs/relocation.c:735
Code: 25 10 f8 f8 43 c6 44 25 12 f8 49 c7 c7 8b ff ff ff e9 69 fd ff ff e8 0d e2 9e fd eb 10 e8 06 e2 9e fd eb 09 e8 ff e1 9e fd 90 <0f> 0b 90 44 89 f9 f7 d9 49 bc 00 00 00 00 00 fc ff df e9 36 fe ff
RSP: 0018:ffffc900058575e0 EFLAGS: 00010293
RAX: ffffffff8427a091 RBX: ffff888052cd0001 RCX: ffff88801aeaca80
RDX: 0000000000000000 RSI: ffffffff8f1e83a0 RDI: 00000000ffffffef
RBP: ffffc90005857740 R08: ffff88801aeaca80 R09: 0000000000000003
R10: 00000000fffffffb R11: 0000000000000000 R12: dffffc0000000000
R13: 1ffff92000b0aec4 R14: ffff888043f5b378 R15: 00000000ffffffef
FS: 00007fc6ff51c6c0(0000) GS:ffff88808c54e000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000003000 CR3: 0000000042b25000 CR4: 0000000000352ef0
Call Trace:
<TASK>
btrfs_init_reloc_root+0x2f0/0x590 fs/btrfs/relocation.c:792
record_root_in_trans+0x27c/0x330 fs/btrfs/transaction.c:462
btrfs_record_root_in_trans+0x15a/0x180 fs/btrfs/transaction.c:508
start_transaction+0x3a6/0x18b0 fs/btrfs/transaction.c:794
btrfs_create_common+0x15c/0x310 fs/btrfs/inode.c:6797
lookup_open fs/namei.c:4508 [inline]
open_last_lookups fs/namei.c:4608 [inline]
path_openat+0x133a/0x3830 fs/namei.c:4860
do_file_open+0x23e/0x4a0 fs/namei.c:4892
do_sys_openat2+0x115/0x200 fs/open.c:1368
do_sys_open fs/open.c:1374 [inline]
__do_sys_openat fs/open.c:1390 [inline]
__se_sys_openat fs/open.c:1385 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1385
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: 0033:0x7fc6fe59de59
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:00007fc6ff51bfe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fc6fe826090 RCX: 00007fc6fe59de59
RDX: 000000000000275a RSI: 0000200000000200 RDI: ffffffffffffff9c
RBP: 00007fc6fe633e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc6fe826128 R14: 00007fc6fe826090 R15: 00007ffc03132988
</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 syzk...@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 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