BTRFS info (device loop0): balance: start -d -m
BTRFS info (device loop0): relocating block group 6881280 flags data|metadata
BTRFS info (device loop0): relocating block group 5242880 flags data|metadata
assertion failed: !cache->nr_nodes, in fs/btrfs/backref.c:3169
------------[ cut here ]------------
kernel BUG at fs/btrfs/backref.c:3169!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5323 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+0x1fb/0x230 fs/btrfs/backref.c:3169
Code: 1f fd 90 0f 0b e8 95 6b bd fd 48 c7 c7 60 89 17 8c 48 c7 c6 e0 90 17 8c 48 c7 c2 00 8a 17 8c b9 61 0c 00 00 e8 36 b8 1f fd 90 <0f> 0b e8 6e 6b bd fd 48 c7 c7 60 89 17 8c 48 c7 c6 20 91 17 8c 48
RSP: 0018:ffffc9000da977a8 EFLAGS: 00010246
RAX: 000000000000003e RBX: ffff888036bf0020 RCX: 69aefc158c019800
RDX: ffffc90020001000 RSI: 00000000000823d8 RDI: 00000000000823d9
RBP: 0000000000000001 R08: ffffc9000da97527 R09: 1ffff92001b52ea4
R10: dffffc0000000000 R11: fffff52001b52ea5 R12: dffffc0000000000
R13: 1ffff11006d7e004 R14: ffff888036bf00f0 R15: ffff888036bf0000
FS:  00007f0dcb9ca6c0(0000) GS:ffff88808ca4f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f57621e0480 CR3: 0000000044bbf000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 relocate_block_group+0xb80/0xe70 fs/btrfs/relocation.c:3625
 do_nonremap_reloc+0xa8/0x5b0 fs/btrfs/relocation.c:5250
 btrfs_relocate_block_group+0x7e6/0xc40 fs/btrfs/relocation.c:5416
 btrfs_relocate_chunk+0x115/0x820 fs/btrfs/volumes.c:3598
 __btrfs_balance+0x1db0/0x2ae0 fs/btrfs/volumes.c:4509
 btrfs_balance+0xaf3/0x11b0 fs/btrfs/volumes.c:4896
 btrfs_ioctl_balance+0x3d3/0x610 fs/btrfs/ioctl.c:3453
 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+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0dcab9c819
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:00007f0dcb9c9fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0dcae16090 RCX: 00007f0dcab9c819
RDX: 0000200000000180 RSI: 00000000c4009420 RDI: 0000000000000006
RBP: 00007f0dcac32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0dcae16128 R14: 00007f0dcae16090 R15: 00007ffe6d8042a8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:btrfs_backref_release_cache+0x1fb/0x230 fs/btrfs/backref.c:3169
Code: 1f fd 90 0f 0b e8 95 6b bd fd 48 c7 c7 60 89 17 8c 48 c7 c6 e0 90 17 8c 48 c7 c2 00 8a 17 8c b9 61 0c 00 00 e8 36 b8 1f fd 90 <0f> 0b e8 6e 6b bd fd 48 c7 c7 60 89 17 8c 48 c7 c6 20 91 17 8c 48
RSP: 0018:ffffc9000da977a8 EFLAGS: 00010246
RAX: 000000000000003e RBX: ffff888036bf0020 RCX: 69aefc158c019800
RDX: ffffc90020001000 RSI: 00000000000823d8 RDI: 00000000000823d9
RBP: 0000000000000001 R08: ffffc9000da97527 R09: 1ffff92001b52ea4
R10: dffffc0000000000 R11: fffff52001b52ea5 R12: dffffc0000000000
R13: 1ffff11006d7e004 R14: ffff888036bf00f0 R15: ffff888036bf0000
FS:  00007f0dcb9ca6c0(0000) GS:ffff88808ca4f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f57621e0480 CR3: 0000000044bbf000 CR4: 0000000000352ef0