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BUG: KCSAN: data-race in fprop_fraction_percpu / percpu_counter_add_batch

read to 0xffffffff86253030 of 8 bytes by task 9808 on cpu 0:
 fprop_fraction_percpu+0x9c/0x1c0 lib/flex_proportions.c:238
 __wb_calc_thresh+0x6f/0x250 mm/page-writeback.c:775
 wb_calc_thresh+0x96/0xc0 mm/page-writeback.c:795
 wb_over_bg_thresh+0x287/0x490 mm/page-writeback.c:1949
 wb_check_background_flush fs/fs-writeback.c:1952 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x3b3/0x970 fs/fs-writeback.c:2078
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffffffff86253030 of 8 bytes by interrupt on cpu 1:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 percpu_counter_add include/linux/percpu_counter.h:55 [inline]
 __fprop_inc_percpu_max+0xb9/0x150 lib/flex_proportions.c:272
 wb_domain_writeout_inc mm/page-writeback.c:581 [inline]
 __wb_writeout_inc mm/page-writeback.c:605 [inline]
 test_clear_page_writeback+0x543/0x790 mm/page-writeback.c:2737
 end_page_writeback+0x9e/0x190 mm/filemap.c:1339
 ext4_finish_bio+0x40d/0x520 fs/ext4/page-io.c:148
 ext4_end_bio+0xd2/0x2f0 fs/ext4/page-io.c:370
 bio_endio+0x2fa/0x400 block/bio.c:1821
 req_bio_endio block/blk-core.c:245 [inline]
 blk_update_request+0x427/0x7b0 block/blk-core.c:1464
 scsi_end_request+0x6b/0x360 drivers/scsi/scsi_lib.c:576
 scsi_io_completion+0x11d/0xc80 drivers/scsi/scsi_lib.c:960
 scsi_finish_command+0x283/0x380 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x259/0x280 drivers/scsi/scsi_lib.c:1476
 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+0x0/0x21
 check_kcov_mode kernel/kcov.c:153 [inline]
 __sanitizer_cov_trace_pc+0x20/0x50 kernel/kcov.c:187
 tomoyo_check_path_number_acl+0x95/0xc0 security/tomoyo/file.c:284
 tomoyo_check_acl+0xf6/0x270 security/tomoyo/domain.c:172
 tomoyo_path_number_perm+0x272/0x3c0 security/tomoyo/file.c:733
 tomoyo_path_mknod+0xe6/0x150 security/tomoyo/tomoyo.c:246
 security_path_mknod+0xc6/0x100 security/security.c:1021
 may_o_create fs/namei.c:3033 [inline]
 lookup_open fs/namei.c:3194 [inline]
 do_last fs/namei.c:3331 [inline]
 path_openat+0x1a3e/0x3580 fs/namei.c:3537
 do_filp_open+0x11e/0x1b0 fs/namei.c:3567
 do_sys_open+0x3b3/0x4f0 fs/open.c:1097
 __do_sys_open fs/open.c:1115 [inline]
 __se_sys_open fs/open.c:1110 [inline]
 __x64_sys_open+0x55/0x70 fs/open.c:1110
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22919 Comm: udevd Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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