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BUG: KCSAN: data-race in test_clear_page_writeback / writeout_period

write to 0xffffffff84176490 of 8 bytes by interrupt on cpu 0:
 writeout_period+0xa6/0xe0 mm/page-writeback.c:623
 call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1421
 expire_timers+0x135/0x240 kernel/time/timer.c:1466
 __run_timers+0x378/0x440 kernel/time/timer.c:1734
 run_timer_softirq+0x2d/0x30 kernel/time/timer.c:1749
 __do_softirq+0x12c/0x26e kernel/softirq.c:558
 invoke_softirq kernel/softirq.c:432 [inline]
 __irq_exit_rcu kernel/softirq.c:636 [inline]
 irq_exit_rcu+0x4e/0xa0 kernel/softirq.c:648
 sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1097
 asm_sysvec_apic_timer_interrupt+0x12/0x20
 kcsan_setup_watchpoint+0x94/0x3f0 kernel/kcsan/core.c:437
 trace_sys_enter include/trace/events/syscalls.h:18 [inline]
 syscall_trace_enter+0x1b7/0x290 kernel/entry/common.c:77
 __syscall_enter_from_user_work kernel/entry/common.c:90 [inline]
 syscall_enter_from_user_mode+0x1c/0x20 kernel/entry/common.c:108
 do_syscall_64+0x25/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff84176490 of 8 bytes by task 1245 on cpu 1:
 wb_domain_writeout_inc mm/page-writeback.c:572 [inline]
 __wb_writeout_inc mm/page-writeback.c:593 [inline]
 test_clear_page_writeback+0x3b6/0x600 mm/page-writeback.c:2789
 end_page_writeback+0xd7/0x1b0 mm/filemap.c:1603
 ext4_finish_bio+0x3e2/0x430 fs/ext4/page-io.c:143
 ext4_release_io_end+0x98/0x200 fs/ext4/page-io.c:158
 ext4_end_io_end fs/ext4/page-io.c:192 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:257 [inline]
 ext4_end_io_rsv_work+0x306/0x360 fs/ext4/page-io.c:271
 process_one_work+0x402/0x910 kernel/workqueue.c:2297
 worker_thread+0x636/0xae0 kernel/workqueue.c:2444
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

value changed: 0x0000000100015e18 -> 0x0000000100015f44

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1245 Comm: kworker/u4:7 Tainted: G        W         5.15.0-rc5-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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