[syzbot] [btrfs?] kernel BUG in populate_free_space_tree (2)

[syzbot <syzbot+884dc4621377ba579a6f@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    3b9b1f8df454 Add linux-next specific files for 20250929
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12785ae2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7658505af38711c6
dashboard link: https://syzkaller.appspot.com/bug?extid=884dc4621377ba579a6f
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=170e2334580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2484efae3582/disk-3b9b1f8d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c39cb0b765cf/vmlinux-3b9b1f8d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5aaf42edc1cb/bzImage-3b9b1f8d.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/8172ca4171ed/mount_0.gz
  fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=13de6942580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+884dc4621377ba579a6f@syzkaller.appspotmail.com

BTRFS warning: 'usebackuproot' is deprecated, use 'rescue=usebackuproot' instead
BTRFS info (device loop3 state M): rebuilding free space tree
assertion failed: ret == 0 :: 0, in fs/btrfs/free-space-tree.c:1115
------------[ cut here ]------------
kernel BUG at fs/btrfs/free-space-tree.c:1115!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 6352 Comm: syz.3.25 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:populate_free_space_tree+0x700/0x710 fs/btrfs/free-space-tree.c:1115
Code: ff ff e8 d3 74 d2 fd 48 c7 c7 80 0a f0 8b 48 c7 c6 60 12 f0 8b 31 d2 48 c7 c1 e0 08 f0 8b 41 b8 5b 04 00 00 e8 81 c1 39 fd 90 <0f> 0b 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90
RSP: 0018:ffffc9000430f780 EFLAGS: 00010246
RAX: 0000000000000043 RBX: ffff88805b709630 RCX: fea61d0e2e79d000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc9000430f8b0 R08: ffffc9000430f4a7 R09: 1ffff92000861e94
R10: dffffc0000000000 R11: fffff52000861e95 R12: 0000000000000001
R13: 1ffff92000861f00 R14: dffffc0000000000 R15: 0000000000000000
FS:  00007f424d9fe6c0(0000) GS:ffff888125afc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd78ad212c0 CR3: 0000000076d68000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 btrfs_rebuild_free_space_tree+0x1ba/0x6d0 fs/btrfs/free-space-tree.c:1364
 btrfs_start_pre_rw_mount+0x128f/0x1bf0 fs/btrfs/disk-io.c:3062
 btrfs_remount_rw fs/btrfs/super.c:1334 [inline]
 btrfs_reconfigure+0xaed/0x2160 fs/btrfs/super.c:1559
 reconfigure_super+0x227/0x890 fs/super.c:1076
 do_remount fs/namespace.c:3279 [inline]
 path_mount+0xd1a/0xfe0 fs/namespace.c:4027
 do_mount fs/namespace.c:4048 [inline]
 __do_sys_mount fs/namespace.c:4236 [inline]
 __se_sys_mount+0x313/0x410 fs/namespace.c:4213
 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: 0033:0x7f424e39066a
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007f424d9fde68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f424d9fdef0 RCX: 00007f424e39066a
RDX: 0000200000000180 RSI: 0000200000000380 RDI: 0000000000000000
RBP: 0000200000000180 R08: 00007f424d9fdef0 R09: 0000000000000020
R10: 0000000000000020 R11: 0000000000000246 R12: 0000200000000380
R13: 00007f424d9fdeb0 R14: 0000000000000000 R15: 00002000000002c0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:populate_free_space_tree+0x700/0x710 fs/btrfs/free-space-tree.c:1115
Code: ff ff e8 d3 74 d2 fd 48 c7 c7 80 0a f0 8b 48 c7 c6 60 12 f0 8b 31 d2 48 c7 c1 e0 08 f0 8b 41 b8 5b 04 00 00 e8 81 c1 39 fd 90 <0f> 0b 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90
RSP: 0018:ffffc9000430f780 EFLAGS: 00010246
RAX: 0000000000000043 RBX: ffff88805b709630 RCX: fea61d0e2e79d000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc9000430f8b0 R08: ffffc9000430f4a7 R09: 1ffff92000861e94
R10: dffffc0000000000 R11: fffff52000861e95 R12: 0000000000000001
R13: 1ffff92000861f00 R14: dffffc0000000000 R15: 0000000000000000
FS:  00007f424d9fe6c0(0000) GS:ffff888125afc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd78ad212c0 CR3: 0000000076d68000 CR4: 00000000003526f0


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