Message-Id: <20220519145823.618983-13-frederic@kernel.org>
Date:   Thu, 19 May 2022 16:58:14 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Phil Auld <pauld@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu Liao <liaoyu15@...wei.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Mark Rutland <mark.rutland@....com>
Subject: [PATCH 12/21] rcu/context-tracking: Remove rcu_irq_enter/exit()

Now rcu_irq_enter/exit() is an unecessary middle call between
ct_irq_enter/exit() and nmi_irq_enter/exit(). Take this opportunity
to remove the former functions and move the comments above them to the
new entrypoints.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@...y.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Nicolas Saenz Julienne <nsaenz@...nel.org>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc: Yu Liao<liaoyu15@...wei.com>
Cc: Phil Auld <pauld@...hat.com>
Cc: Paul Gortmaker<paul.gortmaker@...driver.com>
Cc: Alex Belits <abelits@...vell.com>
---
 include/linux/rcutiny.h   |  4 --
 include/linux/rcutree.h   |  4 --
 kernel/context_tracking.c | 75 ++++++++++++++++++++++++++++++++---
 kernel/rcu/tree.c         | 83 ---------------------------------------
 4 files changed, 69 insertions(+), 97 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index ab7e20dfb07b..5921d9ae7ab5 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -88,10 +88,6 @@ static inline void rcu_cpu_stall_reset(void) { }
 static inline int rcu_jiffies_till_stall_check(void) { return 21 * HZ; }
 static inline void rcu_idle_enter(void) { }
 static inline void rcu_idle_exit(void) { }
-static inline void rcu_irq_enter(void) { }
-static inline void rcu_irq_exit_irqson(void) { }
-static inline void rcu_irq_enter_irqson(void) { }
-static inline void rcu_irq_exit(void) { }
 static inline void rcu_irq_exit_check_preempt(void) { }
 #define rcu_is_idle_cpu(cpu) \
 	(is_idle_task(current) && !in_nmi() && !in_hardirq() && !in_serving_softirq())
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 20dbaa9a3882..cafe3fbf4272 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -49,10 +49,6 @@ void cond_synchronize_rcu(unsigned long oldstate);
 
 void rcu_idle_enter(void);
 void rcu_idle_exit(void);
-void rcu_irq_enter(void);
-void rcu_irq_exit(void);
-void rcu_irq_enter_irqson(void);
-void rcu_irq_exit_irqson(void);
 bool rcu_is_idle_cpu(int cpu);
 
 #ifdef CONFIG_PROVE_RCU
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 120c2864dc95..9177bbfbdedf 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -36,24 +36,87 @@ void ct_idle_exit(void)
 }
 EXPORT_SYMBOL_GPL(ct_idle_exit);
 
+/**
+ * ct_irq_enter - inform RCU that current CPU is entering irq away from idle
+ *
+ * Enter an interrupt handler, which might possibly result in exiting
+ * idle mode, in other words, entering the mode in which read-side critical
+ * sections can occur.  The caller must have disabled interrupts.
+ *
+ * Note that the Linux kernel is fully capable of entering an interrupt
+ * handler that it never exits, for example when doing upcalls to user mode!
+ * This code assumes that the idle loop never does upcalls to user mode.
+ * If your architecture's idle loop does do upcalls to user mode (or does
+ * anything else that results in unbalanced calls to the irq_enter() and
+ * irq_exit() functions), RCU will give you what you deserve, good and hard.
+ * But very infrequently and irreproducibly.
+ *
+ * Use things like work queues to work around this limitation.
+ *
+ * You have been warned.
+ *
+ * If you add or remove a call to ct_irq_enter(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
+ */
 noinstr void ct_irq_enter(void)
 {
-	rcu_irq_enter();
+	lockdep_assert_irqs_disabled();
+	ct_nmi_enter();
 }
 
+/**
+ * ct_irq_exit - inform RCU that current CPU is exiting irq towards idle
+ *
+ * Exit from an interrupt handler, which might possibly result in entering
+ * idle mode, in other words, leaving the mode in which read-side critical
+ * sections can occur.  The caller must have disabled interrupts.
+ *
+ * This code assumes that the idle loop never does anything that might
+ * result in unbalanced calls to irq_enter() and irq_exit().  If your
+ * architecture's idle loop violates this assumption, RCU will give you what
+ * you deserve, good and hard.  But very infrequently and irreproducibly.
+ *
+ * Use things like work queues to work around this limitation.
+ *
+ * You have been warned.
+ *
+ * If you add or remove a call to ct_irq_exit(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
+ */
 noinstr void ct_irq_exit(void)
 {
-	rcu_irq_exit();
+	lockdep_assert_irqs_disabled();
+	ct_nmi_exit();
 }
 
-void ct_irq_enter_irqson(void)
+/*
+ * Wrapper for ct_irq_enter() where interrupts are enabled.
+ *
+ * If you add or remove a call to ct_irq_enter_irqson(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
+ */
+void noinstr ct_irq_enter_irqson(void)
 {
-	rcu_irq_enter_irqson();
+	unsigned long flags;
+
+	raw_local_irq_save(flags);
+	ct_irq_enter();
+	raw_local_irq_restore(flags);
 }
 
-void ct_irq_exit_irqson(void)
+/*
+ * Wrapper for ct_irq_exit() where interrupts are enabled.
+ *
+ * If you add or remove a call to ct_irq_exit_irqson(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
+ */
+void noinstr ct_irq_exit_irqson(void)
 {
-	rcu_irq_exit_irqson();
+	unsigned long flags;
+
+	raw_local_irq_save(flags);
+	ct_irq_exit();
+	raw_local_irq_restore(flags);
 }
 
 noinstr void ct_nmi_enter(void)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c2792b200958..17503a6f7f60 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -793,31 +793,6 @@ noinstr void rcu_nmi_exit(void)
 		rcu_dynticks_task_enter();
 }
 
-/**
- * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
- *
- * Exit from an interrupt handler, which might possibly result in entering
- * idle mode, in other words, leaving the mode in which read-side critical
- * sections can occur.  The caller must have disabled interrupts.
- *
- * This code assumes that the idle loop never does anything that might
- * result in unbalanced calls to irq_enter() and irq_exit().  If your
- * architecture's idle loop violates this assumption, RCU will give you what
- * you deserve, good and hard.  But very infrequently and irreproducibly.
- *
- * Use things like work queues to work around this limitation.
- *
- * You have been warned.
- *
- * If you add or remove a call to rcu_irq_exit(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
-void noinstr rcu_irq_exit(void)
-{
-	lockdep_assert_irqs_disabled();
-	rcu_nmi_exit();
-}
-
 #ifdef CONFIG_PROVE_RCU
 /**
  * rcu_irq_exit_check_preempt - Validate that scheduling is possible
@@ -836,21 +811,6 @@ void rcu_irq_exit_check_preempt(void)
 }
 #endif /* #ifdef CONFIG_PROVE_RCU */
 
-/*
- * Wrapper for rcu_irq_exit() where interrupts are enabled.
- *
- * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
-void noinstr rcu_irq_exit_irqson(void)
-{
-	unsigned long flags;
-
-	raw_local_irq_save(flags);
-	rcu_irq_exit();
-	raw_local_irq_restore(flags);
-}
-
 /*
  * Exit an RCU extended quiescent state, which can be either the
  * idle loop or adaptive-tickless usermode execution.
@@ -1045,49 +1005,6 @@ noinstr void rcu_nmi_enter(void)
 	barrier();
 }
 
-/**
- * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
- *
- * Enter an interrupt handler, which might possibly result in exiting
- * idle mode, in other words, entering the mode in which read-side critical
- * sections can occur.  The caller must have disabled interrupts.
- *
- * Note that the Linux kernel is fully capable of entering an interrupt
- * handler that it never exits, for example when doing upcalls to user mode!
- * This code assumes that the idle loop never does upcalls to user mode.
- * If your architecture's idle loop does do upcalls to user mode (or does
- * anything else that results in unbalanced calls to the irq_enter() and
- * irq_exit() functions), RCU will give you what you deserve, good and hard.
- * But very infrequently and irreproducibly.
- *
- * Use things like work queues to work around this limitation.
- *
- * You have been warned.
- *
- * If you add or remove a call to rcu_irq_enter(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
-noinstr void rcu_irq_enter(void)
-{
-	lockdep_assert_irqs_disabled();
-	rcu_nmi_enter();
-}
-
-/*
- * Wrapper for rcu_irq_enter() where interrupts are enabled.
- *
- * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
-void noinstr rcu_irq_enter_irqson(void)
-{
-	unsigned long flags;
-
-	raw_local_irq_save(flags);
-	rcu_irq_enter();
-	raw_local_irq_restore(flags);
-}
-
 /*
  * Check to see if any future non-offloaded RCU-related work will need
  * to be done by the current CPU, even if none need be done immediately,
-- 
2.25.1

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