[syzbot] [exfat?] WARNING in fat_write_inode

[syzbot <syzbot+4cb66d4011e51657d6b4@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    654ae5d73c05 Merge tag 'drm-fixes-2026-09-05' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=146d68f9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e909ffe6b35dddb7
dashboard link: https://syzkaller.appspot.com/bug?extid=4cb66d4011e51657d6b4
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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-654ae5d7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b52a78a429eb/vmlinux-654ae5d7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ee752e9e76b3/bzImage-654ae5d7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4cb66d4011e51657d6b4@syzkaller.appspotmail.com

------------[ cut here ]------------
!buffer_uptodate(bh)
WARNING: fs/buffer.c:991 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:991, CPU#0: syz.0.0/5320
Modules linked in:
CPU: 0 UID: 0 PID: 5320 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 04/01/2014
RIP: 0010:mark_buffer_dirty+0x299/0x410 fs/buffer.c:991
Code: 4c 89 f7 e8 d9 01 d8 ff 49 8b 3e be 40 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 74 52 fb ff e8 bf 8b 66 ff eb 8c e8 b8 8b 66 ff 90 <0f> 0b 90 e9 a5 fd ff ff e8 aa 8b 66 ff 90 0f 0b 90 e9 cf fd ff ff
RSP: 0018:ffffc9000e3cf850 EFLAGS: 00010293
RAX: ffffffff82614078 RBX: ffff888043def620 RCX: ffff8880003fcb00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffffc9000e3cf901 R08: ffff888043def627 R09: 1ffff110087bdec4
R10: dffffc0000000000 R11: ffffed10087bdec5 R12: 1ffff92001c79f20
R13: ffff888043def620 R14: ffff888041c13410 R15: dffffc0000000000
FS:  00005555923af540(0000) GS:ffff88808c2cd000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000563f7528d660 CR3: 000000004429a000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 __fat_write_inode fs/fat/inode.c:946 [inline]
 fat_write_inode+0x939/0xca0 fs/fat/inode.c:963
 write_inode fs/fs-writeback.c:1608 [inline]
 __writeback_single_inode+0x69d/0x1220 fs/fs-writeback.c:1851
 writeback_single_inode+0x544/0xf70 fs/fs-writeback.c:1926
 sync_inode_metadata+0x122/0x1d0 fs/fs-writeback.c:3100
 writeback_inode fs/fat/inode.c:1916 [inline]
 fat_flush_inodes+0x9b/0x1d0 fs/fat/inode.c:1936
 fat_file_release+0xe0/0x1a0 fs/fat/file.c:180
 __fput+0x418/0xa50 fs/file_table.c:512
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
 exit_to_user_mode_loop+0x204/0x770 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:336 [inline]
 do_syscall_64+0x328/0x520 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f597199e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff8b9d4328 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f5971c27da0 RCX: 00007f597199e159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f5971c27da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007f5971c27cb0 R11: 0000000000000246 R12: 00000000000179c9
R13: 00007f5971c2645c R14: 0000000000017964 R15: 00007fff8b9d4430
 </TASK>


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