Pinning down a blocked task to extract diagnostics

["Paul E. McKenney" <paulmck@kernel.org>]

Hello!

Suppose that I need to extract diagnostics information from a blocked
task, but that I absolutely cannot tolerate this task awakening in the
midst of this extraction process.  Is the following code the right way
to make this work given a task "t"?

	raw_spin_lock_irq(&t->pi_lock);
	if (t->on_rq) {
		/* Task no longer blocked, so ignore it. */
	} else {
		/* Extract consistent diagnostic information. */
	}
	raw_spin_unlock_irq(&t->pi_lock);

It looks like all the wakeup paths acquire ->pi_lock, but I figured I
should actually ask...

							Thanx, Paul