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BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

write to 0xffff888129ccd958 of 8 bytes by interrupt on cpu 1:
 percpu_counter_add_batch+0xbc/0x140 lib/percpu_counter.c:91
 __add_wb_stat include/linux/backing-dev.h:74 [inline]
 inc_wb_stat include/linux/backing-dev.h:79 [inline]
 __wb_writeout_inc mm/page-writeback.c:604 [inline]
 test_clear_page_writeback+0x533/0x7e0 mm/page-writeback.c:2737
 end_page_writeback+0x98/0x180 mm/filemap.c:1317
 ext4_finish_bio+0x430/0x540 fs/ext4/page-io.c:148
 ext4_end_bio+0xc6/0x2d0 fs/ext4/page-io.c:370
 bio_endio+0x2db/0x3e0 block/bio.c:1872
 req_bio_endio block/blk-core.c:245 [inline]
 blk_update_request+0x418/0x7a0 block/blk-core.c:1468
 scsi_end_request+0x6e/0x350 drivers/scsi/scsi_lib.c:576
 scsi_io_completion+0x11e/0xcc0 drivers/scsi/scsi_lib.c:960
 scsi_finish_command+0x283/0x390 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x249/0x270 drivers/scsi/scsi_lib.c:1476
 blk_done_softirq+0x1e6/0x250 block/blk-softirq.c:37
 __do_softirq+0x118/0x34a kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xb5/0xd0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:546 [inline]
 do_IRQ+0x7b/0x120 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x21
 native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60
 arch_safe_halt arch/x86/include/asm/paravirt.h:144 [inline]
 default_idle+0x21/0x170 arch/x86/kernel/process.c:695
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1b7/0x290 kernel/sched/idle.c:269
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:361
 start_secondary+0x164/0x1b0 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242

read to 0xffff888129ccd958 of 8 bytes by task 8643 on cpu 0:
 __wb_update_bandwidth+0xb0/0x3d0 mm/page-writeback.c:1365
 wb_update_bandwidth+0x93/0xc0 mm/page-writeback.c:1399
 wb_writeback+0x21d/0x6a0 fs/fs-writeback.c:1897
 wb_do_writeback fs/fs-writeback.c:2037 [inline]
 wb_workfn+0x215/0x970 fs/fs-writeback.c:2078
 process_one_work+0x424/0x930 kernel/workqueue.c:2264
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2410
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8643 Comm: kworker/u4:3 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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