[syzbot] [fs?] [mm?] linux-next test error: WARNING in __folio_start_writeback

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0f4c93f7eb86 Add linux-next specific files for 20250822
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=172c07bc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=21eed27c0deadb92
dashboard link: https://syzkaller.appspot.com/bug?extid=0630e71306742d4b2aea
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/669ede8f5d66/disk-0f4c93f7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/50feda89fe89/vmlinux-0f4c93f7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/317a0d3516fb/bzImage-0f4c93f7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0630e7...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: ./include/linux/backing-dev.h:243 at inode_to_wb include/linux/backing-dev.h:239 [inline], CPU#1: kworker/u8:6/2949
WARNING: ./include/linux/backing-dev.h:243 at __folio_start_writeback+0x9d5/0xb70 mm/page-writeback.c:3027, CPU#1: kworker/u8:6/2949
Modules linked in:
CPU: 1 UID: 0 PID: 2949 Comm: kworker/u8:6 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:inode_to_wb include/linux/backing-dev.h:239 [inline]
RIP: 0010:__folio_start_writeback+0x9d5/0xb70 mm/page-writeback.c:3027
Code: 28 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 ff e8 ce a2 29 00 49 8b 07 25 ff 3f 00 00 e9 1b fa ff ff e8 7c 04 c6 ff 90 <0f> 0b 90 e9 d6 fb ff ff e8 6e 04 c6 ff 48 c7 c7 a0 f8 5f 8e 4c 89
RSP: 0018:ffffc9000bb06ea0 EFLAGS: 00010293
RAX: ffffffff81fad344 RBX: ffffea00050de8c0 RCX: ffff88802ee29e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000bb07010 R08: ffffc9000bb06f97 R09: 0000000000000000
R10: ffffc9000bb06f80 R11: fffff52001760df3 R12: ffffea00050de8c8
R13: 0000000000000000 R14: ffff888023060880 R15: ffff888023060660
FS: 0000000000000000(0000) GS:ffff8881258c3000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7354907000 CR3: 000000000e338000 CR4: 00000000003526f0
Call Trace:
<TASK>
__block_write_full_folio+0x75f/0xe10 fs/buffer.c:1928
blkdev_writepages+0xd1/0x170 block/fops.c:484
do_writepages+0x32e/0x550 mm/page-writeback.c:2604
__writeback_single_inode+0x145/0xff0 fs/fs-writeback.c:1680
writeback_sb_inodes+0x6c7/0x1010 fs/fs-writeback.c:1976
__writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:2047
wb_writeback+0x44f/0xaf0 fs/fs-writeback.c:2158
wb_check_old_data_flush fs/fs-writeback.c:2262 [inline]
wb_do_writeback fs/fs-writeback.c:2315 [inline]
wb_workfn+0xaef/0xef0 fs/fs-writeback.c:2343
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xade/0x17b0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x47c/0x820 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


---
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[Aleksandr Nogikh]

I've bisected the problem to the following commit:

commit 167f21a81a9c4dbd6970a4ee3853aecad405fa7f (HEAD)
Author: Joanne Koong <joanne...@gmail.com>
Date: Mon Jul 7 16:46:06 2025 -0700

mm: remove BDI_CAP_WRITEBACK_ACCT

There are no users of BDI_CAP_WRITEBACK_ACCT now that fuse doesn't do
its own writeback accounting. This commit removes
BDI_CAP_WRITEBACK_ACCT.

Joanne Koong, could you please take a look at the syzbot report below?

[Joanne Koong]

On Wed, Aug 27, 2025 at 6:45 AM Aleksandr Nogikh <nog...@google.com> wrote:
>
> I've bisected the problem to the following commit:
>
> commit 167f21a81a9c4dbd6970a4ee3853aecad405fa7f (HEAD)
> Author: Joanne Koong <joanne...@gmail.com>
> Date: Mon Jul 7 16:46:06 2025 -0700
>
> mm: remove BDI_CAP_WRITEBACK_ACCT
>
> There are no users of BDI_CAP_WRITEBACK_ACCT now that fuse doesn't do
> its own writeback accounting. This commit removes
> BDI_CAP_WRITEBACK_ACCT.
>
> Joanne Koong, could you please take a look at the syzbot report below?

Hi Aleksandr,

Thanks for bisecting this. This is a duplicate of what Marek reported
in [1]. His patch in [2] fixes the warning getting triggered.

Marek, could you submit your patch formally to the mm tree so it could
be picked up?


Thanks,
Joanne


[1] https://lore.kernel.org/linux-fsdevel/a91010a8-e715-4f3d...@samsung.com/T/#u
[2] https://lore.kernel.org/linux-fsdevel/a91010a8-e715-4f3d...@samsung.com/T/#m3aa6506ee7de302242e64861f8e2199f24e4ad46

[Marek Szyprowski]

On 27.08.2025 18:42, Joanne Koong wrote:
> On Wed, Aug 27, 2025 at 6:45 AM Aleksandr Nogikh <nog...@google.com> wrote:
>> I've bisected the problem to the following commit:
>>
>> commit 167f21a81a9c4dbd6970a4ee3853aecad405fa7f (HEAD)
>> Author: Joanne Koong <joanne...@gmail.com>
>> Date: Mon Jul 7 16:46:06 2025 -0700
>>
>> mm: remove BDI_CAP_WRITEBACK_ACCT
>>
>> There are no users of BDI_CAP_WRITEBACK_ACCT now that fuse doesn't do
>> its own writeback accounting. This commit removes
>> BDI_CAP_WRITEBACK_ACCT.
>>
>> Joanne Koong, could you please take a look at the syzbot report below?
> Hi Aleksandr,
>
> Thanks for bisecting this. This is a duplicate of what Marek reported
> in [1]. His patch in [2] fixes the warning getting triggered.
>
> Marek, could you submit your patch formally to the mm tree so it could
> be picked up?

I've already did that:

https://lore.kernel.org/all/20250826130948.103...@samsung.com/

>
> Thanks,
> Joanne
>
>
> [1] https://lore.kernel.org/linux-fsdevel/a91010a8-e715-4f3d...@samsung.com/T/#u
> [2] https://lore.kernel.org/linux-fsdevel/a91010a8-e715-4f3d...@samsung.com/T/#m3aa6506ee7de302242e64861f8e2199f24e4ad46
>
>> On Fri, Aug 22, 2025 at 12:09 PM syzbot
>> <syzbot+0630e7...@syzkaller.appspotmail.com> wrote:
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit: 0f4c93f7eb86 Add linux-next specific files for 20250822
>>> git tree: linux-next

>>> console output: https://protect2.fireeye.com/v1/url?k=1fb70741-7eccadc9-1fb68c0e-74fe4860018a-55254c3abc8830cc&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fsyzkaller.appspot.com%2Fx%2Flog.txt%3Fx%3D172c07bc580000
>>> kernel config: https://protect2.fireeye.com/v1/url?k=7674b464-170f1eec-76753f2b-74fe4860018a-dc792d3947085adc&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fsyzkaller.appspot.com%2Fx%2F.config%3Fx%3D21eed27c0deadb92
>>> dashboard link: https://protect2.fireeye.com/v1/url?k=cc82c51b-adf96f93-cc834e54-74fe4860018a-15cd3914e26f6b7e&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fsyzkaller.appspot.com%2Fbug%3Fextid%3D0630e71306742d4b2aea

>>> compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
>>>
>>> Downloadable assets:

>>> disk image: https://protect2.fireeye.com/v1/url?k=e6bff250-87c458d8-e6be791f-74fe4860018a-800b933a7034a696&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fstorage.googleapis.com%2Fsyzbot-assets%2F669ede8f5d66%2Fdisk-0f4c93f7.raw.xz
>>> vmlinux: https://protect2.fireeye.com/v1/url?k=2603018e-4778ab06-26028ac1-74fe4860018a-9b89a99c7853c7f0&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fstorage.googleapis.com%2Fsyzbot-assets%2F50feda89fe89%2Fvmlinux-0f4c93f7.xz
>>> kernel image: https://protect2.fireeye.com/v1/url?k=420b962e-23703ca6-420a1d61-74fe4860018a-a965e5c8c6b4614a&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fstorage.googleapis.com%2Fsyzbot-assets%2F317a0d3516fb%2FbzImage-0f4c93f7.xz

>>> See https://protect2.fireeye.com/v1/url?k=d9d7c080-b8ac6a08-d9d64bcf-74fe4860018a-5a4a20c239e4ea82&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fgoo.gl%2FtpsmEJ for more information about syzbot.

>>> syzbot engineers can be reached at syzk...@googlegroups.com.
>>>
>>> syzbot will keep track of this issue. See:

>>> https://protect2.fireeye.com/v1/url?k=03a49fa8-62df3520-03a514e7-74fe4860018a-9a57f917485c2c59&q=1&e=3aa7e54d-e6d6-43e9-ade0-0a94ae0545e0&u=https%3A%2F%2Fgoo.gl%2FtpsmEJ%23status 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
>>>

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.