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BUG: KCSAN: data-race in test_clear_page_writeback / writeout_period

write to 0xffffffff88afad40 of 8 bytes by interrupt on cpu 1:
 writeout_period+0xca/0xf0 mm/page-writeback.c:635
 call_timer_fn+0x58/0x2e0 kernel/time/timer.c:1405
 expire_timers kernel/time/timer.c:1450 [inline]
 __run_timers kernel/time/timer.c:1774 [inline]
 __run_timers kernel/time/timer.c:1741 [inline]
 run_timer_softirq+0xb84/0xbd0 kernel/time/timer.c:1789
 __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]
 smp_apic_timer_interrupt+0xe2/0x270 arch/x86/kernel/apic/apic.c:1140
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:759 [inline]
 kcsan_setup_watchpoint+0x25a/0x440 kernel/kcsan/core.c:542
 should_fail+0x1f7/0x2fd lib/fault-inject.c:106
 __should_failslab+0x82/0xb0 mm/failslab.c:33
 should_failslab+0x5/0xf mm/slab_common.c:1789
 slab_pre_alloc_hook mm/slab.h:569 [inline]
 slab_alloc mm/slab.c:3306 [inline]
 kmem_cache_alloc+0x23/0x5e0 mm/slab.c:3484
 __d_alloc+0x51/0x4a0 fs/dcache.c:1690
 d_alloc+0x48/0x170 fs/dcache.c:1769
 d_alloc_parallel+0x81/0xdf0 fs/dcache.c:2521
 lookup_open fs/namei.c:3008 [inline]
 open_last_lookups fs/namei.c:3155 [inline]
 path_openat+0x1026/0x23d0 fs/namei.c:3343
 do_filp_open+0x11e/0x1b0 fs/namei.c:3373
 do_sys_openat2+0x52e/0x680 fs/open.c:1148
 do_sys_open+0xa2/0x110 fs/open.c:1164
 ksys_open include/linux/syscalls.h:1386 [inline]
 __do_sys_open fs/open.c:1170 [inline]
 __se_sys_open fs/open.c:1168 [inline]
 __x64_sys_open+0x50/0x60 fs/open.c:1168
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff88afad40 of 8 bytes by task 13087 on cpu 0:
 wb_domain_writeout_inc mm/page-writeback.c:584 [inline]
 __wb_writeout_inc mm/page-writeback.c:605 [inline]
 test_clear_page_writeback+0x57f/0x7e0 mm/page-writeback.c:2737
 end_page_writeback+0x98/0x180 mm/filemap.c:1317
 ext4_finish_bio+0x39b/0x460 fs/ext4/page-io.c:146
 ext4_release_io_end+0xc5/0x270 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+0x159/0x400 fs/ext4/page-io.c:274
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13087 Comm: kworker/u4:7 Not tainted 5.7.0-rc1-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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