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BUG: KCSAN: data-race in fprop_new_period / fprop_reflect_period_percpu

read-write to 0xffffffff883d4f38 of 4 bytes by interrupt on cpu 1:
 fprop_new_period+0xaa/0xe0 lib/flex_proportions.c:79
 writeout_period+0x59/0xe0 mm/page-writeback.c:613
 call_timer_fn+0x3a/0x300 kernel/time/timer.c:1792
 expire_timers kernel/time/timer.c:1843 [inline]
 __run_timers kernel/time/timer.c:2408 [inline]
 __run_timer_base+0x417/0x640 kernel/time/timer.c:2419
 run_timer_base kernel/time/timer.c:2428 [inline]
 run_timer_softirq+0x45/0x70 kernel/time/timer.c:2439
 __do_softirq+0xc8/0x285 kernel/softirq.c:554
 invoke_softirq kernel/softirq.c:428 [inline]
 __irq_exit_rcu kernel/softirq.c:633 [inline]
 irq_exit_rcu+0x3c/0x90 kernel/softirq.c:645
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
 sysvec_apic_timer_interrupt+0x73/0x80 arch/x86/kernel/apic/apic.c:1043
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
 __rcu_read_unlock+0x59/0x70 kernel/rcu/tree_plugin.h:433
 rcu_read_unlock include/linux/rcupdate.h:782 [inline]
 inet_twsk_purge+0x458/0x4a0 net/ipv4/inet_timewait_sock.c:321
 dccp_v4_exit_batch+0x1a/0x20 net/dccp/ipv4.c:1042
 ops_exit_list net/core/net_namespace.c:175 [inline]
 cleanup_net+0x4cf/0x830 net/core/net_namespace.c:637
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0x465/0x990 kernel/workqueue.c:3335
 worker_thread+0x526/0x730 kernel/workqueue.c:3416
 kthread+0x1d1/0x210 kernel/kthread.c:388
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

read to 0xffffffff883d4f38 of 4 bytes by task 15443 on cpu 0:
 fprop_reflect_period_percpu+0x22/0x1a0 lib/flex_proportions.c:111
 __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+0x7e/0x1e0 mm/page-writeback.c:584
 __folio_end_writeback+0x21b/0x4a0 mm/page-writeback.c:3017
 folio_end_writeback+0x74/0x1f0 mm/filemap.c:1608
 ext4_finish_bio+0x47b/0x8f0 fs/ext4/page-io.c:145
 ext4_release_io_end+0x8c/0x1f0 fs/ext4/page-io.c:160
 ext4_end_io_end fs/ext4/page-io.c:194 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:259 [inline]
 ext4_end_io_rsv_work+0x2d3/0x370 fs/ext4/page-io.c:273
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0x465/0x990 kernel/workqueue.c:3335
 worker_thread+0x526/0x730 kernel/workqueue.c:3416
 kthread+0x1d1/0x210 kernel/kthread.c:388
 ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

value changed: 0x000000cb -> 0x000000cc

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15443 Comm: kworker/u8:8 Not tainted 6.8.0-syzkaller-11743-ga4145ce1e7bc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
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