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BUG: KCSAN: data-race in __ptrace_unlink / syscall_exit_work

write to 0xffff888091149028 of 4 bytes by task 18870 on cpu 0:
 __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:610 [inline]
 exit_notify kernel/exit.c:650 [inline]
 do_exit+0x13d1/0x16c0 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: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

read to 0xffff888091149028 of 4 bytes by task 18864 on cpu 1:
 ptrace_report_syscall include/linux/tracehook.h:60 [inline]
 tracehook_report_syscall_exit include/linux/tracehook.h:129 [inline]
 arch_syscall_exit_tracehook include/linux/entry-common.h:284 [inline]
 syscall_exit_work+0x7b/0x1d0 kernel/entry/common.c:232
 syscall_exit_to_user_mode_prepare+0x2f/0x40 kernel/entry/common.c:259
 syscall_exit_to_user_mode+0x9/0x30 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: 1 PID: 18864 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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