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BUG: KCSAN: data-race in fprop_reflect_period_percpu / fprop_reflect_period_percpu

write to 0xffff8881088a61c8 of 4 bytes by task 27496 on cpu 0:
 fprop_reflect_period_percpu+0x170/0x1a0 lib/flex_proportions.c:134
 fprop_fraction_percpu+0x98/0x150 lib/flex_proportions.c:156
 __wb_calc_thresh mm/page-writeback.c:875 [inline]
 wb_over_bg_thresh+0x203/0x760 mm/page-writeback.c:2120
 wb_check_background_flush fs/fs-writeback.c:2189 [inline]
 wb_do_writeback fs/fs-writeback.c:2287 [inline]
 wb_workfn+0x643/0x940 fs/fs-writeback.c:2314
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
 worker_thread+0x526/0x730 kernel/workqueue.c:3393
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

read to 0xffff8881088a61c8 of 4 bytes by interrupt 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:560 [inline]
 __wb_writeout_add+0x77/0x1d0 mm/page-writeback.c:584
 __folio_end_writeback+0x215/0x4a0 mm/page-writeback.c:3042
 folio_end_writeback+0x74/0x1f0 mm/filemap.c:1632
 mpage_write_end_io+0x281/0x3a0 fs/mpage.c:72
 bio_endio+0x369/0x410 block/bio.c:1636
 blk_update_request+0x382/0x880 block/blk-mq.c:929
 blk_mq_end_request+0x26/0x50 block/blk-mq.c:1057
 lo_complete_rq+0xce/0x180 drivers/block/loop.c:389
 blk_complete_reqs block/blk-mq.c:1132 [inline]
 blk_done_softirq+0x74/0xb0 block/blk-mq.c:1137
 handle_softirqs+0xc3/0x280 kernel/softirq.c:554
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:928
 smpboot_thread_fn+0x31c/0x4c0 kernel/smpboot.c:164
 kthread+0x1d1/0x210 kernel/kthread.c:389
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0x00000180 -> 0x00000183

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 23 Comm: ksoftirqd/1 Tainted: G        W          6.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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