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BUG: KCSAN: data-race in prepare_signal / ptrace_attach

write to 0xffff888104408030 of 4 bytes by task 17687 on cpu 1:
 ptrace_attach+0x26c/0x590 kernel/ptrace.c:462
 __do_sys_ptrace kernel/ptrace.c:1405 [inline]
 __se_sys_ptrace+0x146/0x2c0 kernel/ptrace.c:1387
 __x64_sys_ptrace+0x55/0x70 kernel/ptrace.c:1387
 x64_sys_call+0x2ee5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:102
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888104408030 of 4 bytes by task 17693 on cpu 0:
 sig_ignored kernel/signal.c:121 [inline]
 prepare_signal+0x450/0x670 kernel/signal.c:935
 __send_signal_locked+0x30/0x760 kernel/signal.c:1053
 send_signal_locked+0x34e/0x3c0 kernel/signal.c:1216
 do_send_sig_info+0x9f/0xf0 kernel/signal.c:1269
 do_send_specific+0xca/0x110 kernel/signal.c:4131
 do_tkill kernel/signal.c:4152 [inline]
 __do_sys_tgkill kernel/signal.c:4171 [inline]
 __se_sys_tgkill kernel/signal.c:4165 [inline]
 __x64_sys_tgkill+0x127/0x160 kernel/signal.c:4165
 x64_sys_call+0x2d22/0x3000 arch/x86/include/generated/asm/syscalls_64.h:235
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 17693 Comm: syz.5.4942 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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