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BUG: KCSAN: data-race in do_exit / exit_mm

write to 0xffff888122781064 of 4 bytes by task 18536 on cpu 1:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 exit_mm+0x18c/0x330 kernel/exit.c:469
 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:159 [inline]
 exit_to_user_mode_prepare+0x124/0x210 kernel/entry/common.c:190
 irqentry_exit_to_user_mode+0x5/0x20 kernel/entry/common.c:278
 irqentry_exit+0xe/0x40 kernel/entry/common.c:366
 asm_sysvec_reschedule_ipi+0x12/0x20 arch/x86/include/asm/idtentry.h:586

read to 0xffff888122781064 of 4 bytes by task 18551 on cpu 0:
 find_alive_thread kernel/exit.c:493 [inline]
 find_new_reaper kernel/exit.c:542 [inline]
 forget_original_parent kernel/exit.c:617 [inline]
 exit_notify kernel/exit.c:650 [inline]
 do_exit+0x7e0/0x16c0 kernel/exit.c:826
 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:159 [inline]
 exit_to_user_mode_prepare+0x124/0x210 kernel/entry/common.c:190
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:265
 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: 18551 Comm: syz-executor.1 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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