sched: Convert pi_lock to raw_spinlock

Convert locks which cannot be sleeping locks in preempt-rt to
raw_spinlocks.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -1409,7 +1409,7 @@ struct task_struct {
 #endif
 
 	/* Protection of the PI data structures: */
-	spinlock_t pi_lock;
+	raw_spinlock_t pi_lock;
 
 #ifdef CONFIG_RT_MUTEXES
 	/* PI waiters blocked on a rt_mutex held by this task */