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

write to 0xffffffff84543338 of 4 bytes by interrupt on cpu 0:
 fprop_new_period+0x100/0x180 lib/flex_proportions.c:83
 writeout_period+0x55/0xe0 mm/page-writeback.c:628
 call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1431
 expire_timers+0x135/0x250 kernel/time/timer.c:1476
 __run_timers+0x358/0x420 kernel/time/timer.c:1745
 run_timer_softirq+0x2d/0x30 kernel/time/timer.c:1760
 __do_softirq+0x12c/0x275 kernel/softirq.c:345
 invoke_softirq kernel/softirq.c:221 [inline]
 __irq_exit_rcu+0xaa/0xb0 kernel/softirq.c:422
 sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
 native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
 arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
 acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline]
 acpi_idle_do_entry drivers/acpi/processor_idle.c:517 [inline]
 acpi_idle_enter+0x25b/0x2e0 drivers/acpi/processor_idle.c:652
 cpuidle_enter_state+0x2b6/0x750 drivers/cpuidle/cpuidle.c:237
 cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:351
 call_cpuidle kernel/sched/idle.c:158 [inline]
 cpuidle_idle_call kernel/sched/idle.c:239 [inline]
 do_idle+0x193/0x230 kernel/sched/idle.c:300
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:397
 rest_init+0xc9/0xd0 init/main.c:721
 arch_call_rest_init+0xa/0xb
 start_kernel+0x59e/0x623 init/main.c:1064
 secondary_startup_64_no_verify+0xb0/0xbb

read to 0xffffffff84543338 of 4 bytes by task 1837 on cpu 1:
 fprop_reflect_period_percpu+0x22/0x1a0 lib/flex_proportions.c:192
 __fprop_inc_percpu lib/flex_proportions.c:222 [inline]
 __fprop_inc_percpu_max+0x3f/0x1f0 lib/flex_proportions.c:271
 wb_domain_writeout_inc mm/page-writeback.c:575 [inline]
 __wb_writeout_inc mm/page-writeback.c:599 [inline]
 test_clear_page_writeback+0x43b/0x640 mm/page-writeback.c:2745
 end_page_writeback+0xd7/0x1b0 mm/filemap.c:1460
 ext4_finish_bio+0x3e2/0x430 fs/ext4/page-io.c:143
 ext4_release_io_end+0x98/0x200 fs/ext4/page-io.c:158
 ext4_end_io_end fs/ext4/page-io.c:192 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:257 [inline]
 ext4_end_io_rsv_work+0x306/0x360 fs/ext4/page-io.c:271
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1837 Comm: kworker/u4:7 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
==================================================================