rcu/nocb: Use appropriate rcu_nocb_lock_irqsave()

Instead of hardcoding IRQ save and nocb lock, use the consolidated
API (and fix a comment as per Valentin Schneider's suggestion).
Reviewed-by: NValentin Schneider <valentin.schneider@arm.com>
Tested-by: NValentin Schneider <valentin.schneider@arm.com>
Tested-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NFrederic Weisbecker <frederic@kernel.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

@@ -2478,12 +2478,11 @@ static void rcu_do_batch(struct rcu_data *rdp)
 	}
 
 	/*
-	 * Extract the list of ready callbacks, disabling to prevent
+	 * Extract the list of ready callbacks, disabling IRQs to prevent
 	 * races with call_rcu() from interrupt handlers.  Leave the
 	 * callback counts, as rcu_barrier() needs to be conservative.
 	 */
-	local_irq_save(flags);
-	rcu_nocb_lock(rdp);
+	rcu_nocb_lock_irqsave(rdp, flags);
 	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
 	pending = rcu_segcblist_n_cbs(&rdp->cblist);
 	div = READ_ONCE(rcu_divisor);
@@ -2546,8 +2545,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
 		}
 	}
 
-	local_irq_save(flags);
-	rcu_nocb_lock(rdp);
+	rcu_nocb_lock_irqsave(rdp, flags);
 	rdp->n_cbs_invoked += count;
 	trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
 			    is_idle_task(current), rcu_is_callbacks_kthread());