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BUG: KCSAN: data-race in __wb_writeout_inc / writeout_period

write to 0xffffffff892d3a18 of 8 bytes by interrupt on cpu 1:
 writeout_period+0xa6/0xe0 mm/page-writeback.c:629
 call_timer_fn+0x30/0x2a0 kernel/time/timer.c:1404
 expire_timers+0x116/0x290 kernel/time/timer.c:1449
 __run_timers+0x443/0x500 kernel/time/timer.c:1773
 run_timer_softirq+0x56/0x60 kernel/time/timer.c:1788
 __do_softirq+0x198/0x360 kernel/softirq.c:292
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 do_softirq_own_stack+0x5d/0x80 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:387 [inline]
 __irq_exit_rcu+0x115/0x120 kernel/softirq.c:417
 sysvec_apic_timer_interrupt+0xba/0xd0 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:596
 native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60
 arch_safe_halt arch/x86/include/asm/paravirt.h:150 [inline]
 acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline]
 acpi_idle_do_entry drivers/acpi/processor_idle.c:525 [inline]
 acpi_idle_enter+0x2ff/0x680 drivers/acpi/processor_idle.c:651
 cpuidle_enter_state+0x245/0x5d0 drivers/cpuidle/cpuidle.c:235
 cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:346
 call_cpuidle kernel/sched/idle.c:126 [inline]
 cpuidle_idle_call kernel/sched/idle.c:214 [inline]
 do_idle+0x229/0x310 kernel/sched/idle.c:276
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:372
 start_secondary+0xe3/0x110 arch/x86/kernel/smpboot.c:268
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

read to 0xffffffff892d3a18 of 8 bytes by task 392 on cpu 0:
 wb_domain_writeout_inc mm/page-writeback.c:578 [inline]
 __wb_writeout_inc+0x60/0x1a0 mm/page-writeback.c:599
 test_clear_page_writeback+0x2ef/0x480 mm/page-writeback.c:2747
 end_page_writeback+0xa7/0x110 mm/filemap.c:1314
 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+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 392 Comm: kworker/u4:3 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
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