==================================================================
BUG: KCSAN: data-race in kthread_is_per_cpu / wb_workfn

write to 0xffff8881001cb0ac of 4 bytes by task 8 on cpu 1:
 wb_workfn+0x221/0x520 fs/fs-writeback.c:2110
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881001cb0ac of 4 bytes by task 42 on cpu 0:
 __to_kthread kernel/kthread.c:101 [inline]
 kthread_is_per_cpu+0x2d/0x80 kernel/kthread.c:540
 can_migrate_task+0xf/0x180 kernel/sched/fair.c:7615
 detach_tasks+0xab/0x380 kernel/sched/fair.c:7779
 load_balance+0x768/0xcc0 kernel/sched/fair.c:9679
 newidle_balance+0x10b/0x310 kernel/sched/fair.c:10643
 pick_next_task_fair+0x37/0x270 kernel/sched/fair.c:7203
 pick_next_task kernel/sched/core.c:4960 [inline]
 __schedule+0x256/0x5b0 kernel/sched/core.c:5111
 schedule+0x67/0x90 kernel/sched/core.c:5226
 worker_thread+0x935/0xae0 kernel/workqueue.c:2442
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 42 Comm: kworker/0:2 Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue:  0x0 (events)
==================================================================