[PATCH 2] utrace-ptrace-mini: introduce the empty ptrace_utrace_ops

[Ananth N Mavinakayanahalli]

On Tue, Aug 25, 2009 at 06:52:44PM +0200, Oleg Nesterov wrote:

...

>  void exit_ptrace(struct task_struct *tracer)
>  {
> -	struct task_struct *p, *n;
> -	LIST_HEAD(ptrace_dead);
> -
> -	write_lock_irq(&tasklist_lock);
> -	list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
> -		if (__ptrace_detach(tracer, p))
> -			list_add(&p->ptrace_entry, &ptrace_dead);
> -	}
> -	write_unlock_irq(&tasklist_lock);
> +	for (;;) {
> +		struct task_struct *tracee = NULL;
> 
> -	BUG_ON(!list_empty(&tracer->ptraced));
> +		read_lock(&tasklist_lock);
> +		if (!list_empty(&tracer->ptraced)) {
> +			tracee = list_first_entry(&tracer->ptraced,
> +					struct task_struct, ptrace_entry);
> +			get_task_struct(tracee);
> +		}
> +		read_unlock(&tasklist_lock);
> +		if (!tracee)
> +			break;

Can tracee be NULL? If so, get_task_struct() shouldn't be called
unconditionally above.

Ananth