linux-kernel - [RFC 1/2] rcu: Do prepare and cleanup idle depending on in

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Date:   Wed, 20 Jun 2018 17:47:19 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     jiangshanlai@...il.com, paulmck@...ux.vnet.ibm.com,
        josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com
Cc:     linux-kernel@...r.kernel.org, kernel-team@....com,
        joel@...lfernandes.org
Subject: [RFC 1/2] rcu: Do prepare and cleanup idle depending on in_nmi()

Get rid of dependency on ->dynticks_nmi_nesting.

Signed-off-by: Byungchul Park <byungchul.park@....com>
---
 kernel/rcu/tree.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index deb2508..59ae94e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -797,6 +797,11 @@ void rcu_nmi_exit(void)
 		return;
 	}
 
+	if (!in_nmi()) {
+		rcu_prepare_for_idle();
+		rcu_dynticks_task_enter();
+	}
+
 	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
 	trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks);
 	WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
@@ -824,14 +829,8 @@ void rcu_nmi_exit(void)
  */
 void rcu_irq_exit(void)
 {
-	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-
 	lockdep_assert_irqs_disabled();
-	if (rdtp->dynticks_nmi_nesting == 1)
-		rcu_prepare_for_idle();
 	rcu_nmi_exit();
-	if (rdtp->dynticks_nmi_nesting == 0)
-		rcu_dynticks_task_enter();
 }
 
 /*
@@ -944,6 +943,11 @@ void rcu_nmi_enter(void)
 	if (rcu_dynticks_curr_cpu_in_eqs()) {
 		rcu_dynticks_eqs_exit();
 		incby = 1;
+
+		if (!in_nmi()) {
+			rcu_dynticks_task_exit();
+			rcu_cleanup_after_idle();
+		}
 	}
 	trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
 			  rdtp->dynticks_nmi_nesting,
@@ -977,14 +981,8 @@ void rcu_nmi_enter(void)
  */
 void rcu_irq_enter(void)
 {
-	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-
 	lockdep_assert_irqs_disabled();
-	if (rdtp->dynticks_nmi_nesting == 0)
-		rcu_dynticks_task_exit();
 	rcu_nmi_enter();
-	if (rdtp->dynticks_nmi_nesting == 1)
-		rcu_cleanup_after_idle();
 }
 
 /*
-- 
1.9.1