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

write to 0xffffffff8418d388 of 4 bytes by interrupt on cpu 1:
 fprop_new_period+0x100/0x180 lib/flex_proportions.c:83
 writeout_period+0x55/0xe0 mm/page-writeback.c:622
 call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1419
 expire_timers+0x135/0x250 kernel/time/timer.c:1464
 __run_timers+0x358/0x420 kernel/time/timer.c:1732
 run_timer_softirq+0x2d/0x30 kernel/time/timer.c:1747
 __do_softirq+0x12c/0x26e kernel/softirq.c:558
 invoke_softirq kernel/softirq.c:432 [inline]
 __irq_exit_rcu+0x9a/0xb0 kernel/softirq.c:636
 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:638
 kcsan_setup_watchpoint+0x8b/0x3e0 kernel/kcsan/core.c:437
 release_pages+0x68/0x8a0 mm/swap.c:904
 free_pages_and_swap_cache+0x1b2/0x1d0 mm/swap_state.c:320
 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:242 [inline]
 tlb_flush_mmu+0x597/0x5f0 mm/mmu_gather.c:249
 zap_pte_range+0xda1/0xe00 mm/memory.c:1432
 zap_pmd_range mm/memory.c:1481 [inline]
 zap_pud_range mm/memory.c:1510 [inline]
 zap_p4d_range mm/memory.c:1531 [inline]
 unmap_page_range+0x2dc/0x3d0 mm/memory.c:1552
 unmap_single_vma+0x157/0x210 mm/memory.c:1597
 unmap_vmas+0xc0/0x170 mm/memory.c:1629
 exit_mmap+0x22d/0x460 mm/mmap.c:3201
 __mmput+0x27/0x1c0 kernel/fork.c:1101
 mmput+0x3d/0x50 kernel/fork.c:1122
 exit_mm+0x2f7/0x3f0 kernel/exit.c:501
 do_exit+0x402/0x1530 kernel/exit.c:812
 do_group_exit+0xa4/0x1a0 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff8418d388 of 4 bytes by task 27841 on cpu 0:
 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:569 [inline]
 __wb_writeout_inc mm/page-writeback.c:593 [inline]
 test_clear_page_writeback+0x37b/0x560 mm/page-writeback.c:2754
 end_page_writeback+0xd7/0x1b0 mm/filemap.c:1548
 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:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0x00000219 -> 0x0000021a

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27841 Comm: kworker/u4:9 Tainted: G        W         5.14.0-rc3-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
==================================================================