linux-kernel - [PATCH tip/core/rcu 8/9] rcu: Add extended-quiescent-state testing advice

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Date:   Wed,  4 Oct 2017 14:29:34 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 8/9] rcu: Add extended-quiescent-state testing advice

If you add or remove calls to rcu_idle_enter(), rcu_user_enter(),
rcu_irq_exit(), rcu_irq_exit_irqson(), rcu_idle_exit(), rcu_user_exit(),
rcu_irq_enter(), rcu_irq_enter_irqson(), rcu_nmi_enter(), or
rcu_nmi_exit(), you should run a full set of tests on a kernel built
with CONFIG_RCU_EQS_DEBUG=y.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0c44c7b42e6d..5186fcea8ba3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -837,6 +837,9 @@ static void rcu_eqs_enter(bool user)
  * We crowbar the ->dynticks_nesting field to zero to allow for
  * the possibility of usermode upcalls having messed up our count
  * of interrupt nesting level during the prior busy period.
+ *
+ * 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)
 {
@@ -852,6 +855,9 @@ void rcu_idle_enter(void)
  * is permitted between this call and rcu_user_exit(). This way the
  * CPU doesn't need to maintain the tick for RCU maintenance purposes
  * when the CPU runs in userspace.
+ *
+ * If you add or remove a call to rcu_user_enter(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_user_enter(void)
 {
@@ -875,6 +881,9 @@ void rcu_user_enter(void)
  * 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 rcu_irq_exit(void)
 {
@@ -899,6 +908,9 @@ void rcu_irq_exit(void)
 
 /*
  * 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 rcu_irq_exit_irqson(void)
 {
@@ -971,6 +983,9 @@ static void rcu_eqs_exit(bool user)
  * allow for the possibility of usermode upcalls messing up our count
  * of interrupt nesting level during the busy period that is just
  * now starting.
+ *
+ * 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)
 {
@@ -987,6 +1002,9 @@ void rcu_idle_exit(void)
  *
  * Exit RCU idle mode while entering the kernel because it can
  * run a RCU read side critical section anytime.
+ *
+ * If you add or remove a call to rcu_user_exit(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_user_exit(void)
 {
@@ -1012,6 +1030,9 @@ void rcu_user_exit(void)
  * 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.
  */
 void rcu_irq_enter(void)
 {
@@ -1037,6 +1058,9 @@ void rcu_irq_enter(void)
 
 /*
  * 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 rcu_irq_enter_irqson(void)
 {
@@ -1055,6 +1079,9 @@ void rcu_irq_enter_irqson(void)
  * that the CPU is active.  This implementation permits nested NMIs, as
  * 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(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_nmi_enter(void)
 {
@@ -1087,6 +1114,9 @@ void rcu_nmi_enter(void)
  * RCU-idle period, update rdtp->dynticks and rdtp->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(), be sure to test
+ * with CONFIG_RCU_EQS_DEBUG=y.
  */
 void rcu_nmi_exit(void)
 {
-- 
2.5.2