Re: [syzbot] [ocfs2?] kernel BUG in ocfs2_write_begin_nolock (2)

[Matthew Wilcox <willy@infradead.org>]

On Wed, Jun 04, 2025 at 10:16:31PM -0700, syzbot wrote:
> ------------[ cut here ]------------
> kernel BUG at fs/ocfs2/aops.c:1389!

That's this one:

                        /* We should already CoW the refcountd extent. */
                        BUG_ON(ext_flags & OCFS2_EXT_REFCOUNTED);

> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 0 UID: 0 PID: 6894 Comm: syz.4.220 Not tainted 6.15.0-next-20250530-syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> RIP: 0010:ocfs2_populate_write_desc fs/ocfs2/aops.c:1389 [inline]
> RIP: 0010:ocfs2_write_begin_nolock+0x42e0/0x4340 fs/ocfs2/aops.c:1687
> Code: 00 eb 05 e8 82 54 28 fe 49 bd 00 00 00 00 00 fc ff df e9 23 fe ff ff e8 fe dc cd 07 e8 69 54 28 fe 90 0f 0b e8 61 54 28 fe 90 <0f> 0b e8 59 54 28 fe 90 0f 0b e8 51 54 28 fe 90 0f 0b e8 49 54 28
> RSP: 0018:ffffc90019b97240 EFLAGS: 00010293
> RAX: ffffffff83980b4f RBX: 0000000000000002 RCX: ffff88802530da00
> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
> RBP: ffffc90019b97800 R08: ffff88802530da00 R09: 0000000000000006
> R10: 00000000fffffffc R11: 0000000000000000 R12: 0000000000000000
> R13: dffffc0000000000 R14: 0000000000000001 R15: ffff88805b968010
> FS:  00005555780fd500(0000) GS:ffff888125c53000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000110c2f56bd CR3: 00000000675d4000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __ocfs2_page_mkwrite fs/ocfs2/mmap.c:93 [inline]
>  ocfs2_page_mkwrite+0x600/0xc40 fs/ocfs2/mmap.c:144
>  do_page_mkwrite+0x14a/0x310 mm/memory.c:3378
>  wp_page_shared mm/memory.c:3779 [inline]
>  do_wp_page+0x268d/0x5800 mm/memory.c:3998
>  handle_pte_fault mm/memory.c:6105 [inline]
>  __handle_mm_fault+0x1144/0x5620 mm/memory.c:6232
>  handle_mm_fault+0x40a/0x8e0 mm/memory.c:6401
>  do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1387
>  handle_page_fault arch/x86/mm/fault.c:1476 [inline]
>  exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
>  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
> RIP: 0033:0x7f79671566ab
> Code: fa 10 73 2d 83 fa 08 73 46 83 fa 04 73 16 83 fa 01 7c 10 8a 0e 74 0a 0f b7 74 16 fe 66 89 74 17 fe 88 0f c3 8b 4c 16 fc 8b 36 <89> 4c 17 fc 89 37 c3 c5 fa 6f 06 c5 fa 6f 4c 16 f0 c5 fa 7f 07 c5
> RSP: 002b:00007fff1cbdc378 EFLAGS: 00010202
> RAX: 00002000000005c0 RBX: 0000000000000004 RCX: 0000000000737562
> RDX: 0000000000000006 RSI: 0000000075622f2e RDI: 00002000000005c0
> RBP: 00007f79673b7ba0 R08: 00007f7967000000 R09: 0000000000000001
> R10: 0000000000000001 R11: 0000000000000009 R12: 00007f79673b5fac
> R13: 00007fff1cbdc470 R14: fffffffffffffffe R15: 00007fff1cbdc490
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:ocfs2_populate_write_desc fs/ocfs2/aops.c:1389 [inline]
> RIP: 0010:ocfs2_write_begin_nolock+0x42e0/0x4340 fs/ocfs2/aops.c:1687
> Code: 00 eb 05 e8 82 54 28 fe 49 bd 00 00 00 00 00 fc ff df e9 23 fe ff ff e8 fe dc cd 07 e8 69 54 28 fe 90 0f 0b e8 61 54 28 fe 90 <0f> 0b e8 59 54 28 fe 90 0f 0b e8 51 54 28 fe 90 0f 0b e8 49 54 28
> RSP: 0018:ffffc90019b97240 EFLAGS: 00010293
> RAX: ffffffff83980b4f RBX: 0000000000000002 RCX: ffff88802530da00
> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000000
> RBP: ffffc90019b97800 R08: ffff88802530da00 R09: 0000000000000006
> R10: 00000000fffffffc R11: 0000000000000000 R12: 0000000000000000
> R13: dffffc0000000000 R14: 0000000000000001 R15: ffff88805b968010
> FS:  00005555780fd500(0000) GS:ffff888125c53000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005561c2044660 CR3: 00000000675d4000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
>