linux-kernel - [RFC][PATCH 5/9] rcu: Fix rcu_idle

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Message-ID: <20220519213421.869214636@infradead.org>
Date:   Thu, 19 May 2022 23:27:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     frederic@...nel.org, paulmck@...nel.org, rjw@...ysocki.net,
        x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        jpoimboe@...nel.org
Subject: [RFC][PATCH 5/9] rcu: Fix rcu_idle_exit()

Current rcu_idle_exit() is terminally broken because it uses
local_irq_{save,restore}(), which are traced which uses RCU.

However, now that all the callers are sure to have IRQs disabled, we
can remove these calls.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/rcu/tree.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -659,7 +659,7 @@ static noinstr void rcu_eqs_enter(bool u
  * If you add or remove a call to rcu_idle_enter(), be sure to test with
  * CONFIG_RCU_EQS_DEBUG=y.
  */
-void rcu_idle_enter(void)
+void noinstr rcu_idle_enter(void)
 {
 	lockdep_assert_irqs_disabled();
 	rcu_eqs_enter(false);
@@ -896,13 +896,10 @@ static void noinstr rcu_eqs_exit(bool us
  * If you add or remove a call to rcu_idle_exit(), be sure to test with
  * CONFIG_RCU_EQS_DEBUG=y.
  */
-void rcu_idle_exit(void)
+void noinstr rcu_idle_exit(void)
 {
-	unsigned long flags;
-
-	local_irq_save(flags);
+	lockdep_assert_irqs_disabled();
 	rcu_eqs_exit(false);
-	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_idle_exit);