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BUG: KCSAN: data-race in fprop_fraction_percpu / percpu_counter_add_batch

read to 0xffff88809e8f9a40 of 8 bytes by task 9884 on cpu 0:
 fprop_fraction_percpu+0x8b/0x1c0 lib/flex_proportions.c:237
 __wb_calc_thresh+0x6f/0x250 mm/page-writeback.c:775
 wb_dirty_limits mm/page-writeback.c:1531 [inline]
 balance_dirty_pages+0x1187/0x1ba0 mm/page-writeback.c:1693
 balance_dirty_pages_ratelimited+0x752/0xb40 mm/page-writeback.c:1913
 generic_perform_write+0x22d/0x320 mm/filemap.c:3341
 __generic_file_write_iter+0x251/0x380 mm/filemap.c:3434
 ext4_file_write_iter+0x1bd/0xa00 fs/ext4/file.c:268
 call_write_iter include/linux/fs.h:1895 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88809e8f9a40 of 8 bytes by interrupt on cpu 1:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 __fprop_inc_percpu_max+0x9a/0x150 lib/flex_proportions.c:271
 wb_domain_writeout_inc mm/page-writeback.c:581 [inline]
 __wb_writeout_inc mm/page-writeback.c:610 [inline]
 test_clear_page_writeback+0x5ca/0x790 mm/page-writeback.c:2737
 end_page_writeback+0x9e/0x190 mm/filemap.c:1339
 ext4_finish_bio+0x40d/0x520 fs/ext4/page-io.c:110
 ext4_end_bio+0xd2/0x320 fs/ext4/page-io.c:334
 bio_endio+0x3a8/0x4f0 block/bio.c:1818
 req_bio_endio block/blk-core.c:242 [inline]
 blk_update_request+0x427/0x7b0 block/blk-core.c:1462
 scsi_end_request+0x6b/0x3e0 drivers/scsi/scsi_lib.c:579
 scsi_io_completion+0x11d/0xc80 drivers/scsi/scsi_lib.c:963
 scsi_finish_command+0x280/0x380 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x259/0x280 drivers/scsi/scsi_lib.c:1477
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 do_IRQ+0x81/0x130 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x19
 arch_local_irq_enable arch/x86/include/asm/paravirt.h:766 [inline]
 __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:168 [inline]
 _raw_spin_unlock_irq+0x4e/0x80 kernel/locking/spinlock.c:199
 spin_unlock_irq include/linux/spinlock.h:388 [inline]
 process_one_work+0x3b5/0x890 kernel/workqueue.c:2242
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 31529 Comm: kworker/u4:0 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn
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