[v6.1] kernel BUG in ext4_mb_use_inode_pa

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f2ddafa93a25 Linux 6.1.166
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=152f975a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b1adc0bfde2d8a4a
dashboard link: https://syzkaller.appspot.com/bug?extid=d5a5b04ce0161e7eb1f9
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=153da8ba580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/28fc2cbac5cf/disk-f2ddafa9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b17a5a214fbc/vmlinux-f2ddafa9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c2564b1203e5/Image-f2ddafa9.gz.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/3ce263042bf9/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=12211806580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d5a5b0...@syzkaller.appspotmail.com

------------[ cut here ]------------
kernel BUG at fs/ext4/mballoc.c:4360!
Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 5593 Comm: syz.1.237 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/26/2026
pstate: 82400005 (Nzcv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : ext4_mb_use_inode_pa+0x550/0x5a0 fs/ext4/mballoc.c:4360
lr : ext4_mb_use_inode_pa+0x550/0x5a0 fs/ext4/mballoc.c:4360
sp : ffff800023de6b40
x29: ffff800023de6b90 x28: ffff0000f68ebaa0 x27: 0000000000000003
x26: 0000000000000201 x25: ffff0000f68eba64 x24: 1fffe0001ed1d74c
x23: dfff800000000000 x22: 00000000ffffffff x21: 1fffe0001c0b1249
x20: 0000000000000002 x19: ffff0000e0589248 x18: ffff800011b8bf60
x17: 1fffe00033ea877e x16: ffff8000082ee970 x15: 0000000000000000
x14: 0000000000000001 x13: 1fffe0001c0b1246 x12: 0000000000ff0100
x11: ff00800008dbeef4 x10: 0000000000000000 x9 : ffff800008dbeef4
x8 : ffff0000d4cdb780 x7 : ffff800008dac99c x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff0000f68eba5c
x2 : ffff0000f68eba60 x1 : 0000000000000003 x0 : 0000000000000002
Call trace:
ext4_mb_use_inode_pa+0x550/0x5a0 fs/ext4/mballoc.c:4360
ext4_mb_use_preallocated+0xc00/0xe34 fs/ext4/mballoc.c:4458
ext4_mb_new_blocks+0x5e4/0x4338 fs/ext4/mballoc.c:5765
ext4_ext_map_blocks+0x1394/0x56f4 fs/ext4/extents.c:4346
ext4_map_blocks+0x860/0x1778 fs/ext4/inode.c:679
_ext4_get_block+0x19c/0x4d8 fs/ext4/inode.c:822
ext4_get_block_unwritten+0x3c/0x110 fs/ext4/inode.c:855
ext4_block_write_begin+0x50c/0x10e4 fs/ext4/inode.c:1124
ext4_write_begin+0x5f4/0x131c fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x348/0x990 fs/ext4/inode.c:3000
generic_perform_write+0x234/0x4f4 mm/filemap.c:3862
ext4_buffered_write_iter+0x2c4/0x528 fs/ext4/file.c:285
ext4_file_write_iter+0x18c/0x1574 fs/ext4/file.c:-1
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x3ec/0x7f0 fs/read_write.c:584
ksys_pwrite64 fs/read_write.c:699 [inline]
__do_sys_pwrite64 fs/read_write.c:709 [inline]
__se_sys_pwrite64 fs/read_write.c:706 [inline]
__arm64_sys_pwrite64+0x174/0x20c fs/read_write.c:706
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
Code: d4210000 97dbb0f4 d4210000 97dbb0f2 (d4210000)
---[ end trace 0000000000000000 ]---


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