[syzbot] [ocfs2?] divide error in ocfs2_block_group_fill (3)

[syzbot <syzbot+fd8af97c7227fe605d95@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    9b332cece987 Merge tag 'nfsd-6.18-1' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=107b85e2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c2d7b4143707d3a0
dashboard link: https://syzkaller.appspot.com/bug?extid=fd8af97c7227fe605d95
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-9b332cec.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/512c0375bad7/vmlinux-9b332cec.xz
kernel image: https://storage.googleapis.com/syzbot-assets/458c8c31cc7b/bzImage-9b332cec.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fd8af97c7227fe605d95@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 32768
=======================================================
WARNING: The mand mount option has been deprecated and
         and is ignored by this kernel. Remove the mand
         option from the mount to silence this warning.
=======================================================
ocfs2: Mounting device (7,0) on (node local, slot 0) with ordered data mode.
Oops: divide error: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5318 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:ocfs2_bg_discontig_add_extent fs/ocfs2/suballoc.c:335 [inline]
RIP: 0010:ocfs2_block_group_fill+0x5bd/0xa70 fs/ocfs2/suballoc.c:386
Code: 34 1a 49 81 c6 50 01 00 00 45 0f b7 3f 49 83 c5 02 4c 89 e8 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 eb 03 00 00 44 89 f8 31 d2 <66> 41 f7 75 00 0f b7 d8 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 84 c0
RSP: 0018:ffffc9000fd362a0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000100000
RDX: 0000000000000000 RSI: 00000000000010fe RDI: 00000000000010ff
RBP: ffffc9000fd363a8 R08: 00313050554f5247 R09: 00313050554f5247
R10: dffffc0000000000 R11: ffffed100a449001 R12: dffffc0000000000
R13: ffff8880334dc2c2 R14: ffff888052248150 R15: 0000000000000000
FS:  00007f73479876c0(0000) GS:ffff88808d301000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 000000004280a000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 ocfs2_block_group_alloc_discontig fs/ocfs2/suballoc.c:634 [inline]
 ocfs2_block_group_alloc fs/ocfs2/suballoc.c:703 [inline]
 ocfs2_reserve_suballoc_bits+0x20a6/0x4640 fs/ocfs2/suballoc.c:834
 ocfs2_reserve_new_metadata_blocks+0x403/0x940 fs/ocfs2/suballoc.c:984
 ocfs2_expand_inline_dir fs/ocfs2/dir.c:2845 [inline]
 ocfs2_extend_dir+0xc76/0x4870 fs/ocfs2/dir.c:3207
 ocfs2_prepare_dir_for_insert+0x2fe8/0x5450 fs/ocfs2/dir.c:4312
 ocfs2_mknod+0x819/0x2050 fs/ocfs2/namei.c:297
 ocfs2_create+0x1a5/0x440 fs/ocfs2/namei.c:676
 vfs_create+0x24e/0x400 fs/namei.c:3493
 do_mknodat+0x3c6/0x4d0 fs/namei.c:4372
 __do_sys_mknod fs/namei.c:4405 [inline]
 __se_sys_mknod fs/namei.c:4403 [inline]
 __x64_sys_mknod+0x8c/0xa0 fs/namei.c:4403
 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: 0033:0x7f7346b8eec9
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:00007f7347987038 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007f7346de5fa0 RCX: 00007f7346b8eec9
RDX: 0000000000000700 RSI: 0000000000000000 RDI: 0000200000000000
RBP: 00007f7346c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7346de6038 R14: 00007f7346de5fa0 R15: 00007fff09db6038
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ocfs2_bg_discontig_add_extent fs/ocfs2/suballoc.c:335 [inline]
RIP: 0010:ocfs2_block_group_fill+0x5bd/0xa70 fs/ocfs2/suballoc.c:386
Code: 34 1a 49 81 c6 50 01 00 00 45 0f b7 3f 49 83 c5 02 4c 89 e8 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 eb 03 00 00 44 89 f8 31 d2 <66> 41 f7 75 00 0f b7 d8 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 84 c0
RSP: 0018:ffffc9000fd362a0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000100000
RDX: 0000000000000000 RSI: 00000000000010fe RDI: 00000000000010ff
RBP: ffffc9000fd363a8 R08: 00313050554f5247 R09: 00313050554f5247
R10: dffffc0000000000 R11: ffffed100a449001 R12: dffffc0000000000
R13: ffff8880334dc2c2 R14: ffff888052248150 R15: 0000000000000000
FS:  00007f73479876c0(0000) GS:ffff88808d301000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 000000004280a000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	34 1a                	xor    $0x1a,%al
   2:	49 81 c6 50 01 00 00 	add    $0x150,%r14
   9:	45 0f b7 3f          	movzwl (%r15),%r15d
   d:	49 83 c5 02          	add    $0x2,%r13
  11:	4c 89 e8             	mov    %r13,%rax
  14:	48 c1 e8 03          	shr    $0x3,%rax
  18:	42 0f b6 04 20       	movzbl (%rax,%r12,1),%eax
  1d:	84 c0                	test   %al,%al
  1f:	0f 85 eb 03 00 00    	jne    0x410
  25:	44 89 f8             	mov    %r15d,%eax
  28:	31 d2                	xor    %edx,%edx
* 2a:	66 41 f7 75 00       	divw   0x0(%r13) <-- trapping instruction
  2f:	0f b7 d8             	movzwl %ax,%ebx
  32:	4c 89 f0             	mov    %r14,%rax
  35:	48 c1 e8 03          	shr    $0x3,%rax
  39:	42 0f b6 04 20       	movzbl (%rax,%r12,1),%eax
  3e:	84 c0                	test   %al,%al


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