Re: [syzbot] [ext4?] WARNING in __folio_mark_dirty (3)

[syzbot <syzbot+b0a0670332b6b3230a0a@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in __folio_mark_dirty

EXT4-fs error (device loop0): ext4_validate_block_bitmap:441: comm syz-executor349: bg 0: block 112: padding at end of block bitmap is not set
EXT4-fs error (device loop0): ext4_map_blocks:778: inode #15: block 3: comm syz-executor349: lblock 3 mapped to illegal pblock 3 (length 1)
EXT4-fs error (device loop0): ext4_ext_remove_space:2955: inode #15: comm syz-executor349: pblk 0 bad header/extent: invalid extent entries - magic f30a, entries 2, max 4(4), depth 0(0)
EXT4_DEBUG: ext4_page_mkwrite called for inode 15, folio index 0, uptodate=0
------------[ cut here ]------------
WARNING: CPU: 1 PID: 11762 at mm/page-writeback.c:2716 __folio_mark_dirty+0x1fb/0xe20 mm/page-writeback.c:2716
Modules linked in:
CPU: 1 UID: 0 PID: 11762 Comm: syz-executor349 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:__folio_mark_dirty+0x1fb/0xe20 mm/page-writeback.c:2716
Code: 3c 38 00 74 08 48 89 df e8 52 a7 26 00 4c 8b 33 4c 89 f6 48 83 e6 08 31 ff e8 d1 ed c4 ff 49 83 e6 08 75 1c e8 66 e8 c4 ff 90 <0f> 0b 90 eb 16 e8 5b e8 c4 ff e9 7e 07 00 00 e8 51 e8 c4 ff eb 05
RSP: 0000:ffffc9000e9079d0 EFLAGS: 00010293
RAX: ffffffff81f9c4ea RBX: ffffea0002ffa540 RCX: ffff88802e261e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff940005ff4a9 R12: ffff8880564f0590
R13: ffff8880564f0588 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000555559bd6380(0000) GS:ffff888126ef6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000440 CR3: 0000000040848000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 block_dirty_folio+0x17a/0x1d0 fs/buffer.c:754
 fault_dirty_shared_page+0x103/0x570 mm/memory.c:3519
 wp_page_shared mm/memory.c:3906 [inline]
 do_wp_page+0x263e/0x4930 mm/memory.c:4109
 handle_pte_fault mm/memory.c:6211 [inline]
 __handle_mm_fault mm/memory.c:6336 [inline]
 handle_mm_fault+0x97c/0x3400 mm/memory.c:6505
 do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x82/0x100 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7f80acffb0c3
Code: 00 00 00 31 c0 e8 ad 43 03 00 bf 02 01 00 00 31 c9 48 ba 40 04 00 00 00 20 00 00 48 b8 2e 2f 66 69 6c 65 30 00 be 9c ff ff ff <48> 89 02 31 c0 e8 83 43 03 00 31 ff e8 1c 76 00 00 66 2e 0f 1f 84
RSP: 002b:00007ffe81efaf50 EFLAGS: 00010246
RAX: 0030656c69662f2e RBX: 0000200000000000 RCX: 0000000000000000
RDX: 0000200000000440 RSI: 00000000ffffff9c RDI: 0000000000000102
RBP: 0000000000000000 R08: 00007ffe81efaf80 R09: 00007ffe81efaf80
R10: 0000000000000e7c R11: 0000000000000246 R12: 00007ffe81efaf6c
R13: 00000000000000e5 R14: 431bde82d7b634db R15: 00007ffe81efafa0
 </TASK>


Tested on:

commit:         fd95357f Merge tag 'sched_ext-for-6.18-rc6-fixes-2' of..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15839742580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=38a0c4cddc846161
dashboard link: https://syzkaller.appspot.com/bug?extid=b0a0670332b6b3230a0a
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12647e0a580000