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BUG: KCSAN: data-race in test_clear_page_writeback / writeout_period

write to 0xffffffff84177490 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+0x368/0x430 kernel/time/timer.c:1734
 run_timer_softirq+0x2d/0x30 kernel/time/timer.c:1749
 __do_softirq+0x12c/0x26e kernel/softirq.c:558
 run_ksoftirqd+0x13/0x20 kernel/softirq.c:920
 smpboot_thread_fn+0x22f/0x330 kernel/smpboot.c:164
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30

read to 0xffffffff84177490 of 8 bytes by task 8 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: 0x00000000ffffda14 -> 0x00000000ffffdb40

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.15.0-rc7-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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