strace lockup when tracing exec in go

[Oleg Nesterov]

On 09/22, Michal Hocko wrote:
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -91,6 +91,10 @@ static int sig_ignored(struct task_struct *t, int sig, bool force)
>  	if (!sig_task_ignored(t, sig, force))
>  		return 0;
>  
> +	/* Do not ignore signals sent from child to the parent */
> +	if (current->ptrace && current->parent == t)
> +		return 0;

This doesn't look right in general, and this can't really help.

This assumes that the tracer will call do_wait() after mm_access()
fails, but this is not necessarily true.

Note also ptrace_attach(), -ERESTARTNOINTR means that the tracer won't
even return to user-space if SIGCHLD is ignored, the tracer will silently
restart the syscall.

Oleg.