[moderation] [mm?] [fs?] KCSAN: data-race in __wb_writeout_add / __wb_writeout_add

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9b0d551bcc05 Merge tag 'pull-misc' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13fa5334580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6ca22b89f03a1ba8
dashboard link: https://syzkaller.appspot.com/bug?extid=2c49944cbd57016ba157
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linux-...@vger.kernel.org linu...@kvack.org wi...@infradead.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/679956c25666/disk-9b0d551b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8c91a7921971/vmlinux-9b0d551b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4d6f0c70b5ee/bzImage-9b0d551b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2c4994...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __wb_writeout_add / __wb_writeout_add

write to 0xffffffff88e67330 of 8 bytes by interrupt on cpu 0:
wb_domain_writeout_add mm/page-writeback.c:572 [inline]
__wb_writeout_add+0x148/0x1b0 mm/page-writeback.c:586
__folio_end_writeback+0x1a0/0x410 mm/page-writeback.c:3004
folio_end_writeback+0x71/0x3d0 mm/filemap.c:1673
ext4_finish_bio+0x459/0x8c0 fs/ext4/page-io.c:144
ext4_end_bio+0x298/0x3b0 fs/ext4/page-io.c:-1
bio_endio+0x37e/0x420 block/bio.c:1673
blk_update_request+0x336/0x730 block/blk-mq.c:998
blk_mq_end_request+0x26/0x50 block/blk-mq.c:1160
lo_complete_rq+0x98/0x140 drivers/block/loop.c:314
blk_complete_reqs block/blk-mq.c:1235 [inline]
blk_done_softirq+0x77/0xb0 block/blk-mq.c:1240
handle_softirqs+0xb7/0x290 kernel/softirq.c:622
run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1063
smpboot_thread_fn+0x32b/0x530 kernel/smpboot.c:160
kthread+0x486/0x510 kernel/kthread.c:463
ret_from_fork+0x11f/0x1b0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff88e67330 of 8 bytes by task 3298 on cpu 1:
wb_domain_writeout_add mm/page-writeback.c:565 [inline]
__wb_writeout_add+0x81/0x1b0 mm/page-writeback.c:586
__folio_end_writeback+0x1a0/0x410 mm/page-writeback.c:3004
folio_end_writeback+0x71/0x3d0 mm/filemap.c:1673
__block_write_full_folio+0x5f3/0x8f0 fs/buffer.c:1949
block_write_full_folio+0x2c2/0x2e0 fs/buffer.c:-1
blkdev_writepages+0x88/0x100 block/fops.c:484
do_writepages+0x1c6/0x310 mm/page-writeback.c:2604
filemap_fdatawrite_wbc mm/filemap.c:389 [inline]
__filemap_fdatawrite_range mm/filemap.c:422 [inline]
__filemap_fdatawrite mm/filemap.c:428 [inline]
filemap_flush+0xe4/0x120 mm/filemap.c:473
sync_blockdev_nowait+0x29/0x40 block/bdev.c:248
sync_filesystem+0xe2/0x190 fs/sync.c:60
generic_shutdown_super+0x44/0x210 fs/super.c:621
kill_block_super+0x2a/0x70 fs/super.c:1722
ext4_kill_sb+0x42/0x80 fs/ext4/super.c:7401
deactivate_locked_super+0x72/0x1c0 fs/super.c:473
deactivate_super+0x97/0xa0 fs/super.c:506
cleanup_mnt+0x269/0x2e0 fs/namespace.c:1327
__cleanup_mnt+0x19/0x20 fs/namespace.c:1334
task_work_run+0x12e/0x1a0 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xed/0x110 kernel/entry/common.c:43
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0x00000000ffff9b77

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3298 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================
EXT4-fs (loop4): unmounting filesystem 00000000-0000-0000-0000-000000000000.


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