linux-kernel - Re: [syzbot] [fs?] [mm?] linux-next test error: WARNING in __folio_start

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Message-ID: <CANp29Y5zWmwXDq1uuzxi43_VXieykD2OOLF12YvBELCUS_Hibg@mail.gmail.com>
Date: Wed, 27 Aug 2025 15:45:16 +0200
From: Aleksandr Nogikh <nogikh@...gle.com>
To: syzbot <syzbot+0630e71306742d4b2aea@...kaller.appspotmail.com>, 
	joannelkoong@...il.com, David Hildenbrand <david@...hat.com>, mszeredi@...hat.com
Cc: akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-next@...r.kernel.org, 
	sfr@...b.auug.org.au, syzkaller-bugs@...glegroups.com, willy@...radead.org
Subject: Re: [syzbot] [fs?] [mm?] linux-next test error: WARNING in __folio_start_writeback

I've bisected the problem to the following commit:

commit 167f21a81a9c4dbd6970a4ee3853aecad405fa7f (HEAD)
Author: Joanne Koong <joannelkoong@...il.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?

On Fri, Aug 22, 2025 at 12:09 PM syzbot
<syzbot+0630e71306742d4b2aea@...kaller.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://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+0630e71306742d4b2aea@...kaller.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>
>
>
> ---
> 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@...glegroups.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:
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>
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>
> If the report is a duplicate of another one, reply with:
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>
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>