Eric, I won't comment the intent, but I too do not understand this idea.
On 07/30, Eric W. Biederman wrote:
>
> [This change requires more work to handle TASK_STOPPED and TASK_TRACED]
Yes. And it is not clear to me how can you solve this.
> [This adds a new lock ordering dependency siglock -> pi_lock -> rq_lock ]
Not really, ttwu() can be safely called with siglock held and it takes
pi_lock + rq_lock. Say, signal_wake_up().
> +int make_task_wakekill(struct task_struct *p)
> +{
> + unsigned long flags;
> + int cpu, success = 0;
> + struct rq_flags rf;
> + struct rq *rq;
> + long state;
> +
> + /* Assumes p != current */
> + preempt_disable();
> + /*
> + * If we are going to change a thread waiting for CONDITION we
> + * need to ensure that CONDITION=1 done by the caller can not be
> + * reordered with p->state check below. This pairs with mb() in
> + * set_current_state() the waiting thread does.
> + */
> + raw_spin_lock_irqsave(&p->pi_lock, flags);
> + smp_mb__after_spinlock();
> + state = p->state;
> +
> + /* FIXME handle TASK_STOPPED and TASK_TRACED */
> + if ((state == TASK_KILLABLE) ||
> + (state == TASK_INTERRUPTIBLE)) {
> + success = 1;
> + cpu = task_cpu(p);
> + rq = cpu_rq(cpu);
> + rq_lock(rq, &rf);
> + p->state = TASK_WAKEKILL;
You can only do this if the task was already deactivated. Just suppose it
is preempted or does something like
set_current_sate(TASK_INTERRUPTIBLE);
if (CONDITION) {
// make_task_wakekill() sets state = TASK_WAKEKILL
__set_current_state(TASK_RUNNING);
return;
}
schedule();
Oleg.
