[PATCH] rcu: Use IRQ_WORK_INIT_HARD() to initialize defer_qs_iw on PREEMPT_RT kernel

[Zqiang]

On non-PREEMPT_RT kernel, the init_irq_work() make the defer_qs_iw irq-work
execute in interrupt context. however, on PREEMPT_RT kernel, the
init_irq_work() make defer_qs_iq irq-work execute in rt-fifo irq_work
kthreads. when system booting, and the CONFIG_RCU_STRICT_GRACE_PERIOD
is enabled, there are a lot of defer_qs_iw irq-work to be processed
in rt-fifo irq_work kthreads, it occupies boot CPU for long time and
cause other kthread cannot get the boot CPU, the boot process occurs
hang. use IRQ_WORK_INIT_HARD() to initialize defer_qs_iw irq-work, can
ensure the defer_qs_iw irq-work always execute in interrupt context,
whether PREEMPT_RT or non PREEMPT_RT kernel.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 3037c2536e1f..cf7bd28af8ef 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -661,7 +661,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
 			    expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
 				// Get scheduler to re-evaluate and call hooks.
 				// If !IRQ_WORK, FQS scan will eventually IPI.
-				init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
+				rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(rcu_preempt_deferred_qs_handler);
 				rdp->defer_qs_iw_pending = true;
 				irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
 			}
-- 
2.25.1