[PATCH v4 07/27] rcu: Make RCU IRQ enter/exit functions rely on in_nmi()

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

From: Paul E. McKenney <paulmck@xxxxxxxxxx>

The rcu_nmi_enter_common() and rcu_nmi_exit_common() functions take an
"irq" parameter that indicates whether these functions are invoked from
an irq handler (irq==true) or an NMI handler (irq==false).  However,
recent changes have applied notrace to a few critical functions such
that rcu_nmi_enter_common() and rcu_nmi_exit_common() many now rely
on in_nmi().  Note that in_nmi() works no differently than before,
but rather that tracing is now prohibited in code regions where in_nmi()
would incorrectly report NMI state.

This commit therefore removes the "irq" parameter and inlines
rcu_nmi_enter_common() and rcu_nmi_exit_common() into rcu_nmi_enter()
and rcu_nmi_exit(), respectively.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/rcu/tree.c |   45 ++++++++++++++-------------------------------
 1 file changed, 14 insertions(+), 31 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -614,16 +614,18 @@ void rcu_user_enter(void)
 }
 #endif /* CONFIG_NO_HZ_FULL */
 
-/*
+/**
+ * rcu_nmi_exit - inform RCU of exit from NMI context
+ *
  * If we are returning from the outermost NMI handler that interrupted an
  * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
  * to let the RCU grace-period handling know that the CPU is back to
  * being RCU-idle.
  *
- * If you add or remove a call to rcu_nmi_exit_common(), be sure to test
+ * If you add or remove a call to rcu_nmi_exit(), be sure to test
  * with CONFIG_RCU_EQS_DEBUG=y.
  */
-static __always_inline void rcu_nmi_exit_common(bool irq)
+void rcu_nmi_exit(void)
 {
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
@@ -651,27 +653,16 @@ static __always_inline void rcu_nmi_exit
 	trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
 	WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
 
-	if (irq)
+	if (!in_nmi())
 		rcu_prepare_for_idle();
 
 	rcu_dynticks_eqs_enter();
 
-	if (irq)
+	if (!in_nmi())
 		rcu_dynticks_task_enter();
 }
 
 /**
- * rcu_nmi_exit - inform RCU of exit from NMI context
- *
- * If you add or remove a call to rcu_nmi_exit(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
-void rcu_nmi_exit(void)
-{
-	rcu_nmi_exit_common(false);
-}
-
-/**
  * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
  *
  * Exit from an interrupt handler, which might possibly result in entering
@@ -693,7 +684,7 @@ void rcu_nmi_exit(void)
 void rcu_irq_exit(void)
 {
 	lockdep_assert_irqs_disabled();
-	rcu_nmi_exit_common(true);
+	rcu_nmi_exit();
 }
 
 /*
@@ -777,7 +768,7 @@ void rcu_user_exit(void)
 #endif /* CONFIG_NO_HZ_FULL */
 
 /**
- * rcu_nmi_enter_common - inform RCU of entry to NMI context
+ * rcu_nmi_enter - inform RCU of entry to NMI context
  * @irq: Is this call from rcu_irq_enter?
  *
  * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
@@ -786,10 +777,10 @@ void rcu_user_exit(void)
  * long as the nesting level does not overflow an int.  (You will probably
  * run out of stack space first.)
  *
- * If you add or remove a call to rcu_nmi_enter_common(), be sure to test
+ * If you add or remove a call to rcu_nmi_enter(), be sure to test
  * with CONFIG_RCU_EQS_DEBUG=y.
  */
-static __always_inline void rcu_nmi_enter_common(bool irq)
+void rcu_nmi_enter(void)
 {
 	long incby = 2;
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
@@ -807,12 +798,12 @@ static __always_inline void rcu_nmi_ente
 	 */
 	if (rcu_dynticks_curr_cpu_in_eqs()) {
 
-		if (irq)
+		if (!in_nmi())
 			rcu_dynticks_task_exit();
 
 		rcu_dynticks_eqs_exit();
 
-		if (irq)
+		if (!in_nmi())
 			rcu_cleanup_after_idle();
 
 		incby = 1;
@@ -834,14 +825,6 @@ static __always_inline void rcu_nmi_ente
 		   rdp->dynticks_nmi_nesting + incby);
 	barrier();
 }
-
-/**
- * rcu_nmi_enter - inform RCU of entry to NMI context
- */
-void rcu_nmi_enter(void)
-{
-	rcu_nmi_enter_common(false);
-}
 NOKPROBE_SYMBOL(rcu_nmi_enter);
 
 /**
@@ -869,7 +852,7 @@ NOKPROBE_SYMBOL(rcu_nmi_enter);
 void rcu_irq_enter(void)
 {
 	lockdep_assert_irqs_disabled();
-	rcu_nmi_enter_common(true);
+	rcu_nmi_enter();
 }
 
 /*