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

From: syzbot <[email-masked]>
Date: Fri, 22 Aug 2025 03:09:27 -0700

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: [email-masked]

------------[ 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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