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BUG: KCSAN: data-race in fprop_reflect_period_percpu / fprop_reflect_period_percpu

write to 0xffff8881025cd9c8 of 4 bytes by task 227 on cpu 0:
 fprop_reflect_period_percpu+0x17c/0x1a0 lib/flex_proportions.c:215
 __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+0x7b/0x1c0 mm/page-writeback.c:599
 test_clear_page_writeback+0x3a4/0x520 mm/page-writeback.c:2745
 end_page_writeback+0xd7/0x260 mm/filemap.c:1494
 ext4_finish_bio+0x429/0x490 fs/ext4/page-io.c:146
 ext4_release_io_end+0x98/0x200 fs/ext4/page-io.c:161
 ext4_end_io_end fs/ext4/page-io.c:195 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:260 [inline]
 ext4_end_io_rsv_work+0x306/0x360 fs/ext4/page-io.c:274
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x635/0xb90 kernel/workqueue.c:2421
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8881025cd9c8 of 4 bytes by interrupt on cpu 1:
 fprop_reflect_period_percpu+0x32/0x1a0 lib/flex_proportions.c:196
 __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+0x7b/0x1c0 mm/page-writeback.c:599
 test_clear_page_writeback+0x3a4/0x520 mm/page-writeback.c:2745
 end_page_writeback+0xd7/0x260 mm/filemap.c:1494
 ext4_finish_bio+0x429/0x490 fs/ext4/page-io.c:146
 ext4_end_bio+0x1ba/0x310 fs/ext4/page-io.c:367
 bio_endio+0x285/0x350 block/bio.c:1450
 req_bio_endio block/blk-core.c:263 [inline]
 blk_update_request+0x4e5/0xb00 block/blk-core.c:1461
 scsi_end_request+0x51/0x470 drivers/scsi/scsi_lib.c:569
 scsi_io_completion+0x104/0xfb0 drivers/scsi/scsi_lib.c:968
 scsi_finish_command+0x263/0x2b0 drivers/scsi/scsi.c:214
 scsi_softirq_done+0xdf/0x440 drivers/scsi/scsi_lib.c:1446
 blk_done_softirq+0x145/0x190 block/blk-mq.c:588
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:343
 asm_call_irq_on_stack+0xf/0x20
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
 do_softirq_own_stack+0x32/0x40 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:226 [inline]
 __irq_exit_rcu+0xb4/0xc0 kernel/softirq.c:420
 common_interrupt+0xb5/0x130 arch/x86/kernel/irq.c:239
 asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:619

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8462 Comm: syz-fuzzer Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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