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

write to 0xffff8881003250ac of 4 bytes by task 473 on cpu 0:
 freezer_do_not_count include/linux/freezer.h:109 [inline]
 freezable_schedule_timeout include/linux/freezer.h:191 [inline]
 kcompactd+0x33e/0xc10 mm/compaction.c:2865
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881003250ac of 4 bytes by interrupt on cpu 1:
 __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
 rebalance_domains+0x1ae/0x2d0 kernel/sched/fair.c:10058
 __do_softirq+0x12c/0x275 kernel/softirq.c:559
 invoke_softirq kernel/softirq.c:433 [inline]
 __irq_exit_rcu+0xa5/0xb0 kernel/softirq.c:637
 sysvec_apic_timer_interrupt+0x32/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1757 Comm: syz-fuzzer Tainted: G        W         5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
print_req_error: 10 callbacks suppressed
blk_update_request: I/O error, dev loop5, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 1 prio class 0
buffer_io_error: 66 callbacks suppressed
Buffer I/O error on dev loop5, logical block 0, lost async page write
blk_update_request: I/O error, dev loop5, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 8 prio class 0
Buffer I/O error on dev loop5, logical block 0, lost async page write
Buffer I/O error on dev loop5, logical block 1, lost async page write
Buffer I/O error on dev loop5, logical block 2, lost async page write
Buffer I/O error on dev loop5, logical block 3, lost async page write
Buffer I/O error on dev loop5, logical block 4, lost async page write
Buffer I/O error on dev loop5, logical block 5, lost async page write
Buffer I/O error on dev loop5, logical block 6, lost async page write
Buffer I/O error on dev loop5, logical block 7, lost async page write
blk_update_request: I/O error, dev loop5, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 1 prio class 0
blk_update_request: I/O error, dev loop5, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 1 prio class 0
blk_update_request: I/O error, dev loop5, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 8 prio class 0
blk_update_request: I/O error, dev loop5, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 8 prio class 0