[syzbot] [bcachefs?] kernel BUG in bch2_btree_repair_topology_recurse

[syzbot <syzbot+9eb4c69fd4d4a1934f3a@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    260f6f4fda93 Merge tag 'drm-next-2025-07-30' of https://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=154669bc580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3e6923811cbcd88f
dashboard link: https://syzkaller.appspot.com/bug?extid=9eb4c69fd4d4a1934f3a
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16d0c834580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10961ca2580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-260f6f4f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/28b1dc006a89/vmlinux-260f6f4f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dcbc50612705/bzImage-260f6f4f.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/f8e958cdbaf9/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9eb4c69fd4d4a1934f3a@syzkaller.appspotmail.com

  btree=alloc level=1 u64s 11 type btree_ptr_v2 SPOS_MAX len 0 ver 0: seq 3a29d24e27fd9a2e written 65534 min_key R 0:0:16777215 durability: 1 ptr: 0:178:0 gen 0
  btree topology error: 
------------[ cut here ]------------
kernel BUG at fs/bcachefs/btree_gc.c:528!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5534 Comm: syz.0.16 Not tainted 6.16.0-syzkaller-08685-g260f6f4fda93 #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:bch2_btree_repair_topology_recurse+0x52dc/0x52e0 fs/bcachefs/btree_gc.c:528
Code: fd 90 0f 0b e8 05 e1 9c fd 90 0f 0b e8 fd e0 9c fd 90 0f 0b e8 f5 e0 9c fd 90 0f 0b e8 ed e0 9c fd 90 0f 0b e8 e5 e0 9c fd 90 <0f> 0b 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f
RSP: 0018:ffffc9000240ea60 EFLAGS: 00010293
RAX: ffffffff8422bbdb RBX: 00000000fffff6e8 RCX: ffff888000292440
RDX: 0000000000000000 RSI: 00000000fffff6e8 RDI: 0000000000000000
RBP: ffffc9000240ef90 R08: ffffffff8fa09237 R09: 1ffffffff1f41246
R10: dffffc0000000000 R11: fffffbfff1f41247 R12: ffff888011db2e00
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88804137c000
FS:  0000555570dd9500(0000) GS:ffff88808d26e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1344372eb8 CR3: 000000001e88d000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 bch2_check_topology+0x692/0xe00 fs/bcachefs/btree_gc.c:602
 bch2_run_recovery_pass fs/bcachefs/recovery_passes.c:484 [inline]
 __bch2_run_recovery_passes+0x392/0x1010 fs/bcachefs/recovery_passes.c:539
 bch2_run_recovery_passes+0x184/0x210 fs/bcachefs/recovery_passes.c:610
 bch2_fs_recovery+0x2690/0x3a50 fs/bcachefs/recovery.c:1016
 bch2_fs_start+0xaaf/0xda0 fs/bcachefs/super.c:1213
 bch2_fs_get_tree+0xb39/0x1520 fs/bcachefs/fs.c:2488
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
 do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
 do_mount fs/namespace.c:4133 [inline]
 __do_sys_mount fs/namespace.c:4344 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4321
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f91ded9014a
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:00007fff349f3738 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fff349f37c0 RCX: 00007f91ded9014a
RDX: 0000200000001000 RSI: 0000200000001040 RDI: 00007fff349f3780
RBP: 0000200000001000 R08: 00007fff349f37c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000001040
R13: 00007fff349f3780 R14: 0000000000004914 R15: 0000200000001080
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:bch2_btree_repair_topology_recurse+0x52dc/0x52e0 fs/bcachefs/btree_gc.c:528
Code: fd 90 0f 0b e8 05 e1 9c fd 90 0f 0b e8 fd e0 9c fd 90 0f 0b e8 f5 e0 9c fd 90 0f 0b e8 ed e0 9c fd 90 0f 0b e8 e5 e0 9c fd 90 <0f> 0b 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f
RSP: 0018:ffffc9000240ea60 EFLAGS: 00010293
RAX: ffffffff8422bbdb RBX: 00000000fffff6e8 RCX: ffff888000292440
RDX: 0000000000000000 RSI: 00000000fffff6e8 RDI: 0000000000000000
RBP: ffffc9000240ef90 R08: ffffffff8fa09237 R09: 1ffffffff1f41246
R10: dffffc0000000000 R11: fffffbfff1f41247 R12: ffff888011db2e00
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88804137c000
FS:  0000555570dd9500(0000) GS:ffff88808d26e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9b6a72b720 CR3: 000000001e88d000 CR4: 0000000000352ef0


---
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 syzkaller@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 syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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