[syzbot] [btrfs?] kernel BUG in btrfs_create_qgroup

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d358e5254674 Merge tag 'for-6.19/dm-changes' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11dc161a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=de48dccdf203ea90
dashboard link: https://syzkaller.appspot.com/bug?extid=803e4cb8245b52928347
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=14eef992580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=102541b4580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-d358e525.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3fa1d04c1a85/vmlinux-d358e525.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a9b253146e36/bzImage-d358e525.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/29e87432b229/mount_0.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=10eef992580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+803e4c...@syzkaller.appspotmail.com

R13: 00007f6d45de5fa0 R14: 00007f6d45de5fa0 R15: 0000000000000003
</TASK>
assertion failed: prealloc == NULL :: 0, in fs/btrfs/qgroup.c:1690
------------[ cut here ]------------
kernel BUG at fs/btrfs/qgroup.c:1690!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5518 Comm: syz.0.17 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_create_qgroup+0x52b/0x530 fs/btrfs/qgroup.c:1690
Code: 24 08 e8 08 f4 6f 07 48 c7 c7 e0 49 d1 8b 48 c7 c6 40 4a d1 8b 31 d2 48 c7 c1 60 46 d1 8b 41 b8 9a 06 00 00 e8 e6 33 39 fd 90 <0f> 0b 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3
RSP: 0018:ffffc900029af540 EFLAGS: 00010246
RAX: 0000000000000042 RBX: 00000000fffffff4 RCX: 4c7ff4269176e000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000100 R08: ffffc900029af267 R09: 1ffff92000535e4c
R10: dffffc0000000000 R11: fffff52000535e4d R12: dffffc0000000000
R13: 1ffff110001f1b1c R14: ffff888000f8d8e0 R15: ffff888038ab4800
FS: 000055557c30d500(0000) GS:ffff88808d22f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb800c6e6c8 CR3: 000000001fd86000 CR4: 0000000000352ef0
Call Trace:
<TASK>
create_pending_snapshot+0x86c/0x3230 fs/btrfs/transaction.c:1748
create_pending_snapshots+0x17c/0x1c0 fs/btrfs/transaction.c:1940
btrfs_commit_transaction+0xf78/0x3b10 fs/btrfs/transaction.c:2430
create_snapshot fs/btrfs/ioctl.c:779 [inline]
btrfs_mksubvol+0xc75/0x12c0 fs/btrfs/ioctl.c:926
btrfs_mksnapshot+0xab/0xf0 fs/btrfs/ioctl.c:968
__btrfs_ioctl_snap_create+0x520/0x730 fs/btrfs/ioctl.c:1232
btrfs_ioctl_snap_create+0x131/0x180 fs/btrfs/ioctl.c:1259
btrfs_ioctl+0x447/0xd00 fs/btrfs/ioctl.c:-1
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/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6d45b8f7c9
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:00007ffc63bd07b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f6d45de5fa0 RCX: 00007f6d45b8f7c9
RDX: 0000200000001600 RSI: 0000000050009401 RDI: 0000000000000003
RBP: 00007ffc63bd0810 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007f6d45de5fa0 R14: 00007f6d45de5fa0 R15: 0000000000000003
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:btrfs_create_qgroup+0x52b/0x530 fs/btrfs/qgroup.c:1690
Code: 24 08 e8 08 f4 6f 07 48 c7 c7 e0 49 d1 8b 48 c7 c6 40 4a d1 8b 31 d2 48 c7 c1 60 46 d1 8b 41 b8 9a 06 00 00 e8 e6 33 39 fd 90 <0f> 0b 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3
RSP: 0018:ffffc900029af540 EFLAGS: 00010246
RAX: 0000000000000042 RBX: 00000000fffffff4 RCX: 4c7ff4269176e000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000100 R08: ffffc900029af267 R09: 1ffff92000535e4c
R10: dffffc0000000000 R11: fffff52000535e4d R12: dffffc0000000000
R13: 1ffff110001f1b1c R14: ffff888000f8d8e0 R15: ffff888038ab4800
FS: 000055557c30d500(0000) GS:ffff88808d22f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000557ea737e138 CR3: 000000001fd86000 CR4: 0000000000352ef0


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