[syzbot] [btrfs?] kernel BUG in btrfs_backref_release_cache (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c107785c7e8d Merge tag 'modules-7.0-rc3.fixes' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12d0ab5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5c49ee0942d1cdb
dashboard link: https://syzkaller.appspot.com/bug?extid=128c98b49b7ffb4c8fa3
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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-c107785c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f3bc281ac705/vmlinux-c107785c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ecd5165e5812/bzImage-c107785c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+128c98...@syzkaller.appspotmail.com

BTRFS info (device loop0): balance: start -d -m
BTRFS info (device loop0): relocating block group 6881280 flags data|metadata
BTRFS info (device loop0): found 1 extents, stage: move data extents
BTRFS info (device loop0): relocating block group 5242880 flags data|metadata
BTRFS info (device loop0): found 10 extents, stage: move data extents
assertion failed: !cache->nr_nodes :: 0, in fs/btrfs/backref.c:3151
------------[ cut here ]------------
kernel BUG at fs/btrfs/backref.c:3151!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5318 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:btrfs_backref_release_cache+0x234/0x260 fs/btrfs/backref.c:3151
Code: 0f 0b e8 6f 74 bd fd 48 c7 c7 e0 96 17 8c 48 c7 c6 00 9e 17 8c 31 d2 48 c7 c1 80 97 17 8c 41 b8 4f 0c 00 00 e8 9d 85 1f fd 90 <0f> 0b e8 45 74 bd fd 48 c7 c7 e0 96 17 8c 48 c7 c6 40 9e 17 8c 31
RSP: 0018:ffffc9000dd477a8 EFLAGS: 00010246
RAX: 0000000000000043 RBX: ffff8880434c6020 RCX: e86cf94f153c5b00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffffc9000dd47527 R09: 1ffff92001ba8ea4
R10: dffffc0000000000 R11: fffff52001ba8ea5 R12: dffffc0000000000
R13: 1ffff11008698c04 R14: ffff8880434c60f0 R15: 1ffff11008698c21
FS: 00007f83542826c0(0000) GS:ffff88808ca56000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055819b279168 CR3: 0000000044955000 CR4: 0000000000352ef0
Call Trace:
<TASK>
relocate_block_group+0xb80/0xe90 fs/btrfs/relocation.c:3628
do_nonremap_reloc+0xa8/0x5b0 fs/btrfs/relocation.c:5251
btrfs_relocate_block_group+0x75b/0xae0 fs/btrfs/relocation.c:5410
btrfs_relocate_chunk+0x10f/0x810 fs/btrfs/volumes.c:3590
__btrfs_balance+0x1dab/0x2ae0 fs/btrfs/volumes.c:4492
btrfs_balance+0xafa/0x11f0 fs/btrfs/volumes.c:4879
btrfs_ioctl_balance+0x3d3/0x610 fs/btrfs/ioctl.c:3445
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+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f835339c799
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:00007f8354281fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f8353616090 RCX: 00007f835339c799
RDX: 0000200000000180 RSI: 00000000c4009420 RDI: 0000000000000006
RBP: 00007f8353432bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8353616128 R14: 00007f8353616090 R15: 00007ffd7d2ef558
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:btrfs_backref_release_cache+0x234/0x260 fs/btrfs/backref.c:3151
Code: 0f 0b e8 6f 74 bd fd 48 c7 c7 e0 96 17 8c 48 c7 c6 00 9e 17 8c 31 d2 48 c7 c1 80 97 17 8c 41 b8 4f 0c 00 00 e8 9d 85 1f fd 90 <0f> 0b e8 45 74 bd fd 48 c7 c7 e0 96 17 8c 48 c7 c6 40 9e 17 8c 31
RSP: 0018:ffffc9000dd477a8 EFLAGS: 00010246
RAX: 0000000000000043 RBX: ffff8880434c6020 RCX: e86cf94f153c5b00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffffc9000dd47527 R09: 1ffff92001ba8ea4
R10: dffffc0000000000 R11: fffff52001ba8ea5 R12: dffffc0000000000
R13: 1ffff11008698c04 R14: ffff8880434c60f0 R15: 1ffff11008698c21
FS: 00007f83542826c0(0000) GS:ffff88808ca56000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055819b279168 CR3: 0000000044955000 CR4: 0000000000352ef0


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