[moderation] [fs?] [mm?] KCSAN: data-race in fprop_reflect_period_percpu / fprop_reflect_period_percpu (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c2da8b3f914f Merge tag 'erofs-for-6.14-rc1' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13f026b0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=38ed74838f409d2c
dashboard link: https://syzkaller.appspot.com/bug?extid=8dabb8e6a4061bf822c6
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
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/29c71a6870ed/disk-c2da8b3f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/04eb3601f535/vmlinux-c2da8b3f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6a6788de4230/bzImage-c2da8b3f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8dabb8...@syzkaller.appspotmail.com

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

write to 0xffff8881013e29c8 of 4 bytes by task 15067 on cpu 0:
fprop_reflect_period_percpu+0x170/0x1a0 lib/flex_proportions.c:134
fprop_fraction_percpu+0x77/0x150 lib/flex_proportions.c:156
__wb_calc_thresh+0x8e/0x2c0 mm/page-writeback.c:935
wb_bg_dirty_limits mm/page-writeback.c:2183 [inline]
domain_over_bg_thresh+0x22c/0x300 mm/page-writeback.c:2197
wb_over_bg_thresh+0xb3/0x110 mm/page-writeback.c:2218
wb_check_background_flush fs/fs-writeback.c:2218 [inline]
wb_do_writeback fs/fs-writeback.c:2316 [inline]
wb_workfn+0x643/0x940 fs/fs-writeback.c:2343
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3317
worker_thread+0x51d/0x6f0 kernel/workqueue.c:3398
kthread+0x4ae/0x520 kernel/kthread.c:464
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffff8881013e29c8 of 4 bytes by task 14183 on cpu 1:
fprop_reflect_period_percpu+0x32/0x1a0 lib/flex_proportions.c:115
__fprop_add_percpu lib/flex_proportions.c:142 [inline]
__fprop_add_percpu_max+0x58/0x180 lib/flex_proportions.c:200
wb_domain_writeout_add mm/page-writeback.c:584 [inline]
__wb_writeout_add+0x77/0x1d0 mm/page-writeback.c:608
__folio_end_writeback+0x20d/0x490 mm/page-writeback.c:3105
folio_end_writeback+0x74/0x1f0 mm/filemap.c:1625
__block_write_full_folio+0x5bf/0x8c0 fs/buffer.c:1920
block_write_full_folio+0x293/0x2b0
write_cache_pages+0x62/0x100 mm/page-writeback.c:2665
blkdev_writepages+0x59/0x90 block/fops.c:458
do_writepages+0x1d8/0x480 mm/page-writeback.c:2708
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+0xe7/0x120 mm/filemap.c:455
sync_blockdev_nowait+0x29/0x40 block/bdev.c:206
sync_filesystem+0xe3/0x190 fs/sync.c:60
generic_shutdown_super+0x46/0x220 fs/super.c:621
kill_block_super+0x2a/0x70 fs/super.c:1710
deactivate_locked_super+0x7d/0x1c0 fs/super.c:473
deactivate_super+0x9f/0xb0 fs/super.c:506
cleanup_mnt+0x268/0x2e0 fs/namespace.c:1413
__cleanup_mnt+0x19/0x20 fs/namespace.c:1420
task_work_run+0x13a/0x1a0 kernel/task_work.c:239
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0xa8/0x120 kernel/entry/common.c:218
do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000004d -> 0x0000004e

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 14183 Comm: syz-executor Not tainted 6.13.0-syzkaller-07644-gc2da8b3f914f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
==================================================================


---
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 syzk...@googlegroups.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:
#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

[syzbot]

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