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BUG: KCSAN: data-race in mm_update_next_owner / rescuer_thread

write to 0xffff88808aef1024 of 4 bytes by task 23202 on cpu 1:
 set_pf_worker kernel/workqueue.c:2338 [inline]
 rescuer_thread+0xb9e/0xbe0 kernel/workqueue.c:2572
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88808aef1024 of 4 bytes by task 23216 on cpu 0:
 mm_update_next_owner+0x1d9/0x4a0 kernel/exit.c:387
 exit_mm+0x2c0/0x330 kernel/exit.c:482
 do_exit+0x40f/0x16c0 kernel/exit.c:793
 do_group_exit+0xcb/0x180 kernel/exit.c:903
 get_signal+0xe9f/0x1650 kernel/signal.c:2757
 arch_do_signal+0x25/0x270 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0x124/0x210 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:267
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23216 Comm: syz-executor.1 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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