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BUG: KCSAN: data-race in find_alive_thread / futex_wait_queue_me

write to 0xffff8880b5ad9024 of 4 bytes by task 11402 on cpu 0:
 freezer_count include/linux/freezer.h:121 [inline]
 freezable_schedule include/linux/freezer.h:173 [inline]
 futex_wait_queue_me+0x1a2/0x290 kernel/futex.c:2705
 futex_wait+0x19b/0x3f0 kernel/futex.c:2811
 do_futex+0xe9/0x18d0 kernel/futex.c:3882
 __do_sys_futex kernel/futex.c:3943 [inline]
 __se_sys_futex kernel/futex.c:3911 [inline]
 __x64_sys_futex+0x2cd/0x3f0 kernel/futex.c:3911
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880b5ad9024 of 4 bytes by task 11396 on cpu 1:
 find_alive_thread+0xdd/0x130 kernel/exit.c:495
 find_new_reaper kernel/exit.c:544 [inline]
 forget_original_parent kernel/exit.c:619 [inline]
 exit_notify kernel/exit.c:652 [inline]
 do_exit+0x7bd/0x18a0 kernel/exit.c:822
 do_group_exit+0xb4/0x1c0 kernel/exit.c:899
 get_signal+0x2a2/0x1320 kernel/signal.c:2734
 do_signal+0x2f/0x6c0 arch/x86/kernel/signal.c:813
 exit_to_usermode_loop+0x250/0x2c0 arch/x86/entry/common.c:160
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11396 Comm: syz-executor.3 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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