Re: [PATCH v2 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT

[Oleg Nesterov]

On 04/21, Peter Zijlstra wrote:
>
> @@ -1329,8 +1337,7 @@ SYSCALL_DEFINE4(ptrace, long, request, l
>  		goto out_put_task_struct;
>  
>  	ret = arch_ptrace(child, request, addr, data);
> -	if (ret || request != PTRACE_DETACH)
> -		ptrace_unfreeze_traced(child);
> +	ptrace_unfreeze_traced(child);

Forgot to mention... whatever we do this doesn't look right.

ptrace_unfreeze_traced() must not be called if the tracee was untraced,
anothet debugger can come after that. I agree, the current code looks
a bit confusing, perhaps it makes sense to re-write it:

	if (request == PTRACE_DETACH && ret == 0)
		; /* nothing to do, no longer traced by us */
	else
		ptrace_unfreeze_traced(child);

Oleg.