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BUG: KCSAN: data-race in __ptrace_unlink / do_exit

write to 0xffff88809f68a068 of 4 bytes by task 25297 on cpu 1:
 __ptrace_unlink+0x160/0x300 kernel/ptrace.c:132
 __ptrace_detach+0x1b/0x1a0 kernel/ptrace.c:528
 exit_ptrace+0x93/0x160 kernel/ptrace.c:588
 forget_original_parent kernel/exit.c:609 [inline]
 exit_notify kernel/exit.c:649 [inline]
 do_exit+0x1411/0x16e0 kernel/exit.c:826
 do_group_exit+0xcb/0x180 kernel/exit.c:903
 get_signal+0xdee/0x1520 kernel/signal.c:2739
 do_signal+0x25/0x270 arch/x86/kernel/signal.c:810
 exit_to_usermode_loop arch/x86/entry/common.c:212 [inline]
 __prepare_exit_to_usermode+0x127/0x230 arch/x86/entry/common.c:246
 __syscall_return_slowpath+0x47/0x60 arch/x86/entry/common.c:329
 do_syscall_64+0x5d/0xb0 arch/x86/entry/common.c:368
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88809f68a068 of 4 bytes by task 25295 on cpu 0:
 ptrace_event_enabled include/linux/ptrace.h:142 [inline]
 ptrace_event include/linux/ptrace.h:157 [inline]
 do_exit+0x13c/0x16e0 kernel/exit.c:746
 do_group_exit+0xcb/0x180 kernel/exit.c:903
 get_signal+0xdee/0x1520 kernel/signal.c:2739
 do_signal+0x25/0x270 arch/x86/kernel/signal.c:810
 exit_to_usermode_loop arch/x86/entry/common.c:212 [inline]
 __prepare_exit_to_usermode+0x127/0x230 arch/x86/entry/common.c:246
 __syscall_return_slowpath+0x47/0x60 arch/x86/entry/common.c:329
 do_syscall_64+0x5d/0xb0 arch/x86/entry/common.c:368
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25295 Comm: syz-executor.3 Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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