On 11/02, Sebastian Andrzej Siewior wrote:
>
> On 2020-11-02 16:50:01 [+0100], Oleg Nesterov wrote:
> >
> > static void ptrace_unfreeze_traced(struct task_struct *task)
> > {
> > - if (task->state != __TASK_TRACED)
> > - return;
> > + bool frozen = true;
>
> Is this okay for !PREEMPT_RT or is this considered as an important
> fast-path on !PREEMPT_RT?
I do not know how can ptrace_unfreeze_traced() check both ->state and
->saved_state lockless.
If it is possible then task_is_traced() can avoid pi_lock too?
> > WARN_ON(!task->ptrace || task->parent != current);
> >
> > @@ -207,12 +206,19 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
> > * Recheck state under the lock to close this race.
> > */
> > spin_lock_irq(&task->sighand->siglock);
> > - if (task->state == __TASK_TRACED) {
> > - if (__fatal_signal_pending(task))
> > - wake_up_state(task, __TASK_TRACED);
> > - else
> > - task->state = TASK_TRACED;
> > - }
> > +
> > + raw_spin_lock(&task->pi_lock);
>
> I think this got mentioned in the other emails but this requires irqsave
> because the above (siglock) does not disable interrupts on RT.
OK, I'll send V2 in a minute.
> This `saved_state' is only used for RT so it might make sense to avoid
> the PI-lock on non-RT.
The same is true for ptrace_freeze_traced(), we can probably add ifdef's
but I am not sure this makes sense...
Oleg.
