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BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

write to 0xffff888102591940 of 8 bytes by interrupt on cpu 1:
 percpu_counter_add_batch+0x9c/0xd0 lib/percpu_counter.c:91
 __add_wb_stat include/linux/backing-dev.h:70 [inline]
 inc_wb_stat include/linux/backing-dev.h:75 [inline]
 __wb_writeout_inc mm/page-writeback.c:592 [inline]
 test_clear_page_writeback+0x34d/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_end_bio+0x1ba/0x310 fs/ext4/page-io.c:364
 bio_endio+0x2d4/0x300 block/bio.c:1413
 req_bio_endio block/blk-core.c:263 [inline]
 blk_update_request+0x435/0xa40 block/blk-core.c:1438
 scsi_end_request+0x4d/0x450 drivers/scsi/scsi_lib.c:540
 scsi_io_completion+0xdb/0x10d0 drivers/scsi/scsi_lib.c:936
 scsi_finish_command+0x1d0/0x1e0 drivers/scsi/scsi.c:207
 scsi_complete+0x1c0/0x1f0 drivers/scsi/scsi_lib.c:1425
 blk_complete_reqs block/blk-mq.c:577 [inline]
 blk_done_softirq+0x69/0x90 block/blk-mq.c:582
 __do_softirq+0x12c/0x26e kernel/softirq.c:558
 invoke_softirq kernel/softirq.c:432 [inline]
 __irq_exit_rcu+0x9a/0xb0 kernel/softirq.c:636
 common_interrupt+0x78/0x90 arch/x86/kernel/irq.c:240
 asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:629
 native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
 arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
 acpi_safe_halt drivers/acpi/processor_idle.c:109 [inline]
 acpi_idle_do_entry drivers/acpi/processor_idle.c:553 [inline]
 acpi_idle_enter+0x258/0x2e0 drivers/acpi/processor_idle.c:688
 cpuidle_enter_state+0x2b6/0x750 drivers/cpuidle/cpuidle.c:237
 cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:351
 call_cpuidle kernel/sched/idle.c:158 [inline]
 cpuidle_idle_call kernel/sched/idle.c:239 [inline]
 do_idle+0x1a3/0x240 kernel/sched/idle.c:306
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 secondary_startup_64_no_verify+0xb0/0xbb

read to 0xffff888102591940 of 8 bytes by task 17559 on cpu 0:
 percpu_counter_read include/linux/percpu_counter.h:72 [inline]
 __wb_update_bandwidth+0x9f/0x480 mm/page-writeback.c:1353
 wb_update_bandwidth+0x4e/0x70 mm/page-writeback.c:1387
 wb_writeback+0x421/0x700 fs/fs-writeback.c:2056
 wb_check_old_data_flush fs/fs-writeback.c:2155 [inline]
 wb_do_writeback+0x461/0x510 fs/fs-writeback.c:2208
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2237
 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: 0x0000000000004e30 -> 0x0000000000004e40

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 17559 Comm: kworker/u4:2 Not tainted 5.14.0-rc3-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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