[syzbot] [btrfs?] kernel BUG in replace_file_extents

[syzbot <syzbot+3e20d8f3d41bac5dc9a2@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    43cfbdda5af6 Merge tag 'for-linus-iommufd' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14fb82d2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=eae4973b8684a00c
dashboard link: https://syzkaller.appspot.com/bug?extid=3e20d8f3d41bac5dc9a2
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-43cfbdda.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/473adbf1a380/vmlinux-43cfbdda.xz
kernel image: https://storage.googleapis.com/syzbot-assets/63ebea9fbab4/bzImage-43cfbdda.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3e20d8f3d41bac5dc9a2@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): relocating block group 5242880 flags data|metadata
BTRFS info (device loop0): found 22 extents, stage: move data extents
------------[ cut here ]------------
kernel BUG at fs/btrfs/relocation.c:841!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5328 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:get_new_location fs/btrfs/relocation.c:838 [inline]
RIP: 0010:replace_file_extents+0x1574/0x1590 fs/btrfs/relocation.c:941
Code: 81 2c fe 49 8b 3e be 03 00 00 00 48 c7 c2 40 da 17 8c 44 89 e9 e8 cc dd 25 fd e8 f7 36 ff ff e9 a7 fc ff ff e8 ad 5f c0 fd 90 <0f> 0b e8 a5 5f c0 fd 90 0f 0b e8 9d 5f c0 fd 90 0f 0b e8 95 5f c0
RSP: 0000:ffffc900071f6e80 EFLAGS: 00010287
RAX: ffffffff8404c563 RBX: ffff88800e57f9a0 RCX: 0000000000100000
RDX: ffffc90021003000 RSI: 00000000000c282c RDI: 00000000000c282d
RBP: ffffc900071f7090 R08: ffffea0000ef04c7 R09: 1ffffd40001de098
R10: dffffc0000000000 R11: fffff940001de099 R12: 0000000000000483
R13: ffff88805b2e8000 R14: 0000000000000e70 R15: 80c06030180c2811
FS:  00007fa6cd9886c0(0000) GS:ffff88808c820000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2a6cc8ecf0 CR3: 000000001cdeb000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 btrfs_force_cow_block+0xa4d/0x2450 fs/btrfs/ctree.c:532
 btrfs_cow_block+0x3c4/0xa90 fs/btrfs/ctree.c:699
 do_relocation+0xd2e/0x1920 fs/btrfs/relocation.c:2288
 relocate_tree_block fs/btrfs/relocation.c:2538 [inline]
 relocate_tree_blocks+0x11ee/0x2020 fs/btrfs/relocation.c:2645
 relocate_block_group+0x76f/0xe70 fs/btrfs/relocation.c:3570
 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: 0033:0x7fa6ccb9c819
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:00007fa6cd987fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa6cce16090 RCX: 00007fa6ccb9c819
RDX: 0000200000000180 RSI: 00000000c4009420 RDI: 0000000000000006
RBP: 00007fa6ccc32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa6cce16128 R14: 00007fa6cce16090 R15: 00007ffdf45f3438
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:get_new_location fs/btrfs/relocation.c:838 [inline]
RIP: 0010:replace_file_extents+0x1574/0x1590 fs/btrfs/relocation.c:941
Code: 81 2c fe 49 8b 3e be 03 00 00 00 48 c7 c2 40 da 17 8c 44 89 e9 e8 cc dd 25 fd e8 f7 36 ff ff e9 a7 fc ff ff e8 ad 5f c0 fd 90 <0f> 0b e8 a5 5f c0 fd 90 0f 0b e8 9d 5f c0 fd 90 0f 0b e8 95 5f c0
RSP: 0000:ffffc900071f6e80 EFLAGS: 00010287
RAX: ffffffff8404c563 RBX: ffff88800e57f9a0 RCX: 0000000000100000
RDX: ffffc90021003000 RSI: 00000000000c282c RDI: 00000000000c282d
RBP: ffffc900071f7090 R08: ffffea0000ef04c7 R09: 1ffffd40001de098
R10: dffffc0000000000 R11: fffff940001de099 R12: 0000000000000483
R13: ffff88805b2e8000 R14: 0000000000000e70 R15: 80c06030180c2811
FS:  00007fa6cd9886c0(0000) GS:ffff88808c820000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557e0c9528 CR3: 000000001cdeb000 CR4: 0000000000352ef0


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