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BUG: KCSAN: data-race in prepare_signal / ptrace_attach

write to 0xffff888102844130 of 4 bytes by task 12893 on cpu 0:
 ptrace_attach+0x26a/0x420 kernel/ptrace.c:445
 __do_sys_ptrace kernel/ptrace.c:1296 [inline]
 __se_sys_ptrace+0x149/0x2a0 kernel/ptrace.c:1278
 __x64_sys_ptrace+0x55/0x60 kernel/ptrace.c:1278
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888102844130 of 4 bytes by task 12895 on cpu 1:
 prepare_signal+0x258/0x660 kernel/signal.c:943
 __send_signal_locked+0x2f/0x700 kernel/signal.c:1094
 send_signal_locked+0x28d/0x3a0 kernel/signal.c:1257
 do_send_sig_info+0x9f/0xf0 kernel/signal.c:1310
 group_send_sig_info kernel/signal.c:1460 [inline]
 kill_pid_info+0x86/0xd0 kernel/signal.c:1499
 kill_proc_info kernel/signal.c:1516 [inline]
 do_rt_sigqueueinfo kernel/signal.c:4035 [inline]
 __do_sys_rt_sigqueueinfo kernel/signal.c:4051 [inline]
 __se_sys_rt_sigqueueinfo+0xc7/0x110 kernel/signal.c:4044
 __x64_sys_rt_sigqueueinfo+0x43/0x50 kernel/signal.c:4044
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x00000000 -> 0x00010001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12895 Comm: syz-executor.3 Not tainted 6.6.0-syzkaller-14142-g90b0c2b2edd1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
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