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BUG: KCSAN: data-race in __ptrace_unlink / syscall_trace_enter

write to 0xffff88814195e0f0 of 4 bytes by task 6346 on cpu 0:
 __ptrace_unlink+0x162/0x320 kernel/ptrace.c:132
 __ptrace_detach+0x1b/0x1d0 kernel/ptrace.c:522
 exit_ptrace+0x93/0x160 kernel/ptrace.c:582
 forget_original_parent kernel/exit.c:628 [inline]
 exit_notify kernel/exit.c:668 [inline]
 do_exit+0x126d/0x1560 kernel/exit.c:845
 do_group_exit+0xa4/0x1a0 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814195e0f0 of 4 bytes by task 6344 on cpu 1:
 ptrace_report_syscall include/linux/tracehook.h:60 [inline]
 tracehook_report_syscall_entry include/linux/tracehook.h:105 [inline]
 arch_syscall_enter_tracehook include/linux/entry-common.h:98 [inline]
 syscall_trace_enter+0x4d/0x290 kernel/entry/common.c:60
 __syscall_enter_from_user_work kernel/entry/common.c:89 [inline]
 syscall_enter_from_user_mode+0x1c/0x20 kernel/entry/common.c:107
 do_syscall_64+0x11/0x50 arch/x86/entry/common.c:41
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6344 Comm: syz-executor.5 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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