rcu: Remove local_irq_save/restore() in rcu_preempt_deferred_qs_handler()

The per-CPU rcu_data structure's ->defer_qs_iw field is initialized
by IRQ_WORK_INIT_HARD(), which means that the subsequent invocation of
rcu_preempt_deferred_qs_handler() will always be executed with interrupts
disabled.  This commit therefore removes the local_irq_save/restore()
operations from rcu_preempt_deferred_qs_handler() and adds a call to
lockdep_assert_irqs_disabled() in order to enable lockdep to diagnose
mistaken invocations of this function from interrupts-enabled code.

Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: Zqiang

kernel/rcu/tree_plugin.h

@@ -626,11 +626,10 @@ notrace void rcu_preempt_deferred_qs(struct task_struct *t)
  */
 static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
 {
-	unsigned long flags;
 	struct rcu_data *rdp;
 
+	lockdep_assert_irqs_disabled();
 	rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
-	local_irq_save(flags);
 
 	/*
 	 * If the IRQ work handler happens to run in the middle of RCU read-side
@@ -647,8 +646,6 @@ static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
 	 */
 	if (rcu_preempt_depth() > 0)
 		WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE);
-
-	local_irq_restore(flags);
 }
 
 /*