On 08/27, Ananth N Mavinakayanahalli wrote:
>
> 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.
tracee == NULL when list_empty(->ptraced) == T. get_task_struct()
is called when we know we do have tracees,
if (!list_empty()) {
tracee = list_first_entry();
get_task_struct(tracee);
}
in that case tracee != NULL
Oleg.
