[PATCH -tip 19/32] entry/idle: Enter and exit kernel protection during idle entry and exit

[Joel Fernandes (Google)]

Add a generic_idle_{enter,exit} helper function to enter and exit kernel
protection when entering and exiting idle, respectively.

While at it, remove a stale RCU comment.

Reviewed-by: Alexandre Chartre <alexandre.char...@oracle.com>
Tested-by: Julien Desfossez <jdesfos...@digitalocean.com>
Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
---
 include/linux/entry-common.h | 18 ++++++++++++++++++
 kernel/sched/idle.c          | 11 ++++++-----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 022e1f114157..8f34ae625f83 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -454,4 +454,22 @@ static inline bool entry_kernel_protected(void)
        return IS_ENABLED(CONFIG_SCHED_CORE) && sched_core_kernel_protected()
                && _TIF_UNSAFE_RET != 0;
 }
+
+/**
+ * generic_idle_enter - General tasks to perform during idle entry.
+ */
+static inline void generic_idle_enter(void)
+{
+       /* Entering idle ends the protected kernel region. */
+       sched_core_unsafe_exit();
+}
+
+/**
+ * generic_idle_exit  - General tasks to perform during idle exit.
+ */
+static inline void generic_idle_exit(void)
+{
+       /* Exiting idle (re)starts the protected kernel region. */
+       sched_core_unsafe_enter();
+}
 #endif
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8bdb214eb78f..ee4f91396c31 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -8,6 +8,7 @@
  */
 #include "sched.h"
 
+#include <linux/entry-common.h>
 #include <trace/events/power.h>
 
 /* Linker adds these: start and end of __cpuidle functions */
@@ -54,6 +55,7 @@ __setup("hlt", cpu_idle_nopoll_setup);
 
 static noinline int __cpuidle cpu_idle_poll(void)
 {
+       generic_idle_enter();
        trace_cpu_idle(0, smp_processor_id());
        stop_critical_timings();
        rcu_idle_enter();
@@ -66,6 +68,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
        rcu_idle_exit();
        start_critical_timings();
        trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
+       generic_idle_exit();
 
        return 1;
 }
@@ -156,11 +159,7 @@ static void cpuidle_idle_call(void)
                return;
        }
 
-       /*
-        * The RCU framework needs to be told that we are entering an idle
-        * section, so no more rcu read side critical sections and one more
-        * step to the grace period
-        */
+       generic_idle_enter();
 
        if (cpuidle_not_available(drv, dev)) {
                tick_nohz_idle_stop_tick();
@@ -225,6 +224,8 @@ static void cpuidle_idle_call(void)
         */
        if (WARN_ON_ONCE(irqs_disabled()))
                local_irq_enable();
+
+       generic_idle_exit();
 }
 
 /*
-- 
2.29.2.299.gdc1121823c-goog