linux-kernel - [syzbot] [btrfs?] kernel BUG in modify_free_space

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Message-ID: <691b2afb.a70a0220.f6df1.000f.GAE@google.com>
Date: Mon, 17 Nov 2025 06:02:35 -0800
From: syzbot <syzbot+2b448e5301f0d29f3d39@...kaller.appspotmail.com>
To: clm@...com, dsterba@...e.com, josef@...icpanda.com, 
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: [syzbot] [btrfs?] kernel BUG in modify_free_space_bitmap

Hello,

syzbot found the following issue on:

HEAD commit:    e927c520e1ba Merge tag 'loongarch-fixes-6.18-1' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=127f897c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=929790bc044e87d7
dashboard link: https://syzkaller.appspot.com/bug?extid=2b448e5301f0d29f3d39
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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-e927c520.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/924fb782edf1/vmlinux-e927c520.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7e6af189c28e/bzImage-e927c520.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2b448e5301f0d29f3d39@...kaller.appspotmail.com

loop0: detected capacity change from 0 to 32768
BTRFS: device fsid 395ef67a-297e-477c-816d-cd80a5b93e5d devid 1 transid 8 /dev/loop0 (7:0) scanned by syz.0.0 (5332)
BTRFS info (device loop0): first mount of filesystem 395ef67a-297e-477c-816d-cd80a5b93e5d
BTRFS info (device loop0): using sha256 (sha256-lib) checksum algorithm
BTRFS info (device loop0): enabling ssd optimizations
BTRFS info (device loop0): turning on async discard
BTRFS info (device loop0): enabling free space tree
netlink: 830 bytes leftover after parsing attributes in process `syz.0.0'.
BTRFS info (device loop0 state M): rebuilding free space tree
assertion failed: key.type == BTRFS_FREE_SPACE_BITMAP_KEY :: 0, in fs/btrfs/free-space-tree.c:556
------------[ cut here ]------------
kernel BUG at fs/btrfs/free-space-tree.c:556!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5332 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~bpo12+1 04/01/2014
RIP: 0010:free_space_modify_bits fs/btrfs/free-space-tree.c:556 [inline]
RIP: 0010:modify_free_space_bitmap+0xbd6/0xc10 fs/btrfs/free-space-tree.c:665
Code: 0f 0b e8 5d 7c cf fd 48 c7 c7 e0 6e b0 8b 48 c7 c6 00 72 b0 8b 31 d2 48 c7 c1 40 6d b0 8b 41 b8 2c 02 00 00 e8 ab fa 36 fd 90 <0f> 0b e8 33 7c cf fd 48 c7 c7 e0 6e b0 8b 48 c7 c6 20 73 b0 8b 31
RSP: 0018:ffffc9000d43f5a0 EFLAGS: 00010246
RAX: 0000000000000061 RBX: 00000000000000c6 RCX: ab56fb4df2ad8d00
RDX: ffffc9000deea000 RSI: 0000000000002135 RDI: 0000000000002136
RBP: ffffc9000d43f770 R08: ffffc9000d43f2c7 R09: 1ffff92001a87e58
R10: dffffc0000000000 R11: fffff52001a87e59 R12: ffff888051083800
R13: dffffc0000000000 R14: 0000000000006000 R15: ffff888052afad10
FS:  00007f39159f26c0(0000) GS:ffff88808d730000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffdf4c5d158 CR3: 0000000040118000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 populate_free_space_tree+0x38d/0x600 fs/btrfs/free-space-tree.c:1129
 btrfs_rebuild_free_space_tree+0x1ba/0x6d0 fs/btrfs/free-space-tree.c:1365
 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:4029
 do_mount fs/namespace.c:4050 [inline]
 __do_sys_mount fs/namespace.c:4238 [inline]
 __se_sys_mount+0x313/0x410 fs/namespace.c:4215
 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: 0033:0x7f3914b90e6a
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:00007f39159f1e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f39159f1ef0 RCX: 00007f3914b90e6a
RDX: 0000200000000180 RSI: 0000200000000100 RDI: 0000000000000000
RBP: 0000200000000180 R08: 00007f39159f1ef0 R09: 0000000000ad0c24
R10: 0000000000ad0c24 R11: 0000000000000246 R12: 0000200000000100
R13: 00007f39159f1eb0 R14: 0000000000000000 R15: 00002000000002c0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:free_space_modify_bits fs/btrfs/free-space-tree.c:556 [inline]
RIP: 0010:modify_free_space_bitmap+0xbd6/0xc10 fs/btrfs/free-space-tree.c:665
Code: 0f 0b e8 5d 7c cf fd 48 c7 c7 e0 6e b0 8b 48 c7 c6 00 72 b0 8b 31 d2 48 c7 c1 40 6d b0 8b 41 b8 2c 02 00 00 e8 ab fa 36 fd 90 <0f> 0b e8 33 7c cf fd 48 c7 c7 e0 6e b0 8b 48 c7 c6 20 73 b0 8b 31
RSP: 0018:ffffc9000d43f5a0 EFLAGS: 00010246
RAX: 0000000000000061 RBX: 00000000000000c6 RCX: ab56fb4df2ad8d00
RDX: ffffc9000deea000 RSI: 0000000000002135 RDI: 0000000000002136
RBP: ffffc9000d43f770 R08: ffffc9000d43f2c7 R09: 1ffff92001a87e58
R10: dffffc0000000000 R11: fffff52001a87e59 R12: ffff888051083800
R13: dffffc0000000000 R14: 0000000000006000 R15: ffff888052afad10
FS:  00007f39159f26c0(0000) GS:ffff88808d730000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffdf4c5d158 CR3: 0000000040118000 CR4: 0000000000352ef0


---
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