Message-ID: <68f765e7.050a0220.346f24.0012.GAE@google.com>
Date: Tue, 21 Oct 2025 03:52:23 -0700
From: syzbot <syzbot+6dafaff006dcd512c3af@...kaller.appspotmail.com>
To: clm@...com, dsterba@...e.com, josef@...icpanda.com, 
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: [syzbot] [btrfs?] kernel BUG in btrfs_backref_release_cache (2)

Hello,

syzbot found the following issue on:

HEAD commit:    98ac9cc4b445 Merge tag 'f2fs-fix-6.18-rc2' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15facb04580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c2d7b4143707d3a0
dashboard link: https://syzkaller.appspot.com/bug?extid=6dafaff006dcd512c3af
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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-98ac9cc4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4a2afc96e189/vmlinux-98ac9cc4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/92d24cde05de/bzImage-98ac9cc4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6dafaff006dcd512c3af@...kaller.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 9 extents, stage: move data extents
assertion failed: !cache->nr_nodes :: 0, in fs/btrfs/backref.c:3160
------------[ cut here ]------------
kernel BUG at fs/btrfs/backref.c:3160!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5319 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~bpo12+1 04/01/2014
RIP: 0010:btrfs_backref_release_cache+0x1ef/0x220 fs/btrfs/backref.c:3160
Code: 0f 0b e8 84 5f d7 fd 48 c7 c7 80 16 b0 8b 48 c7 c6 20 1f b0 8b 31 d2 48 c7 c1 20 17 b0 8b 41 b8 58 0c 00 00 e8 22 9d 3e fd 90 <0f> 0b e8 5a 5f d7 fd 48 c7 c7 80 16 b0 8b 48 c7 c6 60 1f b0 8b 31
RSP: 0018:ffffc9000d5c7830 EFLAGS: 00010246
RAX: 0000000000000043 RBX: ffff88801f4f2020 RCX: 85e0f5a888a8ee00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bfa650 R12: 1ffff11003e9e421
R13: 00000000fffffffe R14: ffff88801f4f20f0 R15: dffffc0000000000
FS:  00007faaa33d86c0(0000) GS:ffff88808d300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5176a4e949 CR3: 000000001fd36000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 relocate_block_group+0xac6/0xd70 fs/btrfs/relocation.c:3638
 btrfs_relocate_block_group+0x6bc/0xc60 fs/btrfs/relocation.c:3983
 btrfs_relocate_chunk+0x12f/0x5c0 fs/btrfs/volumes.c:3451
 __btrfs_balance+0x1860/0x23f0 fs/btrfs/volumes.c:4227
 btrfs_balance+0xac2/0x11b0 fs/btrfs/volumes.c:4604
 btrfs_ioctl_balance+0x3d3/0x610 fs/btrfs/ioctl.c:3577
 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+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faaa258efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007faaa33d8038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007faaa27e6090 RCX: 00007faaa258efc9
RDX: 0000200000000180 RSI: 00000000c4009420 RDI: 0000000000000005
RBP: 00007faaa2611f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007faaa27e6128 R14: 00007faaa27e6090 R15: 00007ffe79b9d7c8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:btrfs_backref_release_cache+0x1ef/0x220 fs/btrfs/backref.c:3160
Code: 0f 0b e8 84 5f d7 fd 48 c7 c7 80 16 b0 8b 48 c7 c6 20 1f b0 8b 31 d2 48 c7 c1 20 17 b0 8b 41 b8 58 0c 00 00 e8 22 9d 3e fd 90 <0f> 0b e8 5a 5f d7 fd 48 c7 c7 80 16 b0 8b 48 c7 c6 60 1f b0 8b 31
RSP: 0018:ffffc9000d5c7830 EFLAGS: 00010246
RAX: 0000000000000043 RBX: ffff88801f4f2020 RCX: 85e0f5a888a8ee00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000002 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bfa650 R12: 1ffff11003e9e421
R13: 00000000fffffffe R14: ffff88801f4f20f0 R15: dffffc0000000000
FS:  00007faaa33d86c0(0000) GS:ffff88808d300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5176a5bae0 CR3: 000000001fd36000 CR4: 0000000000352ef0


---
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