[PATCH 3.16 321/328] cpuidle: Do not access cpuidle_devices when !CONFIG_CPU_IDLE

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Catalin Marinas <catalin.marinas@xxxxxxx>

commit 9bd616e3dbedfc103f158197c8ad93678849b1ed upstream.

The cpuidle_devices per-CPU variable is only defined when CPU_IDLE is
enabled. Commit c8cc7d4de7a4 ("sched/idle: Reorganize the idle loop")
removed the #ifdef CONFIG_CPU_IDLE around cpuidle_idle_call() with the
compiler optimising away __this_cpu_read(cpuidle_devices). However, with
CONFIG_UBSAN && !CONFIG_CPU_IDLE, this optimisation no longer happens
and the kernel fails to link since cpuidle_devices is not defined.

This patch introduces an accessor function for the current CPU cpuidle
device (returning NULL when !CONFIG_CPU_IDLE) and uses it in
cpuidle_idle_call().

Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 include/linux/cpuidle.h | 3 +++
 kernel/sched/idle.c     | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -146,6 +146,8 @@ extern int cpuidle_play_dead(void);
 extern void cpuidle_use_deepest_state(bool enable);
 
 extern struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev);
+static inline struct cpuidle_device *cpuidle_get_device(void)
+{return __this_cpu_read(cpuidle_devices); }
 #else
 static inline void disable_cpuidle(void) { }
 static inline int cpuidle_select(struct cpuidle_driver *drv,
@@ -179,6 +181,7 @@ static inline int cpuidle_play_dead(void
 static inline void cpuidle_use_deepest_state(bool enable) {}
 static inline struct cpuidle_driver *cpuidle_get_cpu_driver(
 	struct cpuidle_device *dev) {return NULL; }
+static inline struct cpuidle_device *cpuidle_get_device(void) {return NULL; }
 #endif
 
 #ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -76,7 +76,7 @@ void __weak arch_cpu_idle(void)
  */
 static void cpuidle_idle_call(void)
 {
-	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
+	struct cpuidle_device *dev = cpuidle_get_device();
 	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
 	int next_state, entered_state;
 	bool broadcast;