powercap: idle_inject: Replace zero-length array with flexible-array …

…member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

Lastly, fix the following checkpatch warning:
WARNING: Prefer 'unsigned long' over 'unsigned long int' as the int is unnecessary
+	unsigned long int cpumask[];

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] KSPP/linux#21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Rsyd58 <[email protected]>

drivers/powercap/Makefile

@@ -1,3 +1,2 @@
-obj-$(CONFIG_POWERCAP)	+= powercap_sys.o
 obj-$(CONFIG_INTEL_RAPL) += intel_rapl.o
 obj-$(CONFIG_IDLE_INJECT) += idle_inject.o

drivers/powercap/idle_inject.c

@@ -44,7 +44,7 @@
 #include <linux/slab.h>
 #include <linux/smpboot.h>
 
-#include <uapi/linux/sched/types.h>
+//#include <uapi/linux/sched/types.h>
 
 /**
  * struct idle_inject_thread - task on/off switch structure
@@ -67,7 +67,7 @@ struct idle_inject_device {
 	struct hrtimer timer;
 	unsigned int idle_duration_us;
 	unsigned int run_duration_us;
-	unsigned long int cpumask[0];
+	unsigned long cpumask[];
 };
 
 static DEFINE_PER_CPU(struct idle_inject_thread, idle_inject_thread);

drivers/thermal/Makefile

@@ -18,7 +18,8 @@ thermal_sys-$(CONFIG_THERMAL_GOV_LOW_LIMITS) += gov_low_limits.o
 thermal_sys-$(CONFIG_THERMAL_GOV_POWER_ALLOCATOR)	+= power_allocator.o
 
 # cpufreq cooling
-thermal_sys-$(CONFIG_CPU_THERMAL)	+= cpu_cooling.o
+thermal_sys-$(CONFIG_CPU_THERMAL)	+= cpufreq_cooling.o
+thermal_sys-$(CONFIG_CPU_IDLE_THERMAL)	+= cpuidle_cooling.o
 
 # clock cooling
 thermal_sys-$(CONFIG_CLOCK_THERMAL)	+= clock_cooling.o

include/linux/cpuidle.h

@@ -151,6 +151,7 @@ extern void cpuidle_resume(void);
 extern int cpuidle_enable_device(struct cpuidle_device *dev);
 extern void cpuidle_disable_device(struct cpuidle_device *dev);
 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)

kernel/sched/idle.c

@@ -315,7 +315,7 @@ void play_idle(unsigned long duration_us)
 
 	rcu_sleep_check();
 	preempt_disable();
-	current->flags |= PF_IDLE;
+	current->flags |= PF_WAKE_UP_IDLE;
 	cpuidle_use_deepest_state(true);
 
 	it.done = 0;
@@ -325,10 +325,10 @@ void play_idle(unsigned long duration_us)
 		      HRTIMER_MODE_REL_PINNED);
 
 	while (!READ_ONCE(it.done))
-		do_idle();
+		cpu_idle_loop();
 
 	cpuidle_use_deepest_state(false);
-	current->flags &= ~PF_IDLE;
+	current->flags &= ~PF_WAKE_UP_IDLE;
 
 	preempt_fold_need_resched();
 	preempt_enable();
@@ -357,115 +357,3 @@ void cpu_startup_entry(enum cpuhp_state state)
 	cpu_idle_loop();
 }
 
-/*
- * idle-task scheduling class.
- */
-
-#ifdef CONFIG_SMP
-static int
-select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)
-{
-	return task_cpu(p); /* IDLE tasks as never migrated */
-}
-#endif
-
-/*
- * Idle tasks are unconditionally rescheduled:
- */
-static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
-{
-	resched_curr(rq);
-}
-
-static struct task_struct *
-pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
-{
-	put_prev_task(rq, prev);
-	update_idle_core(rq);
-	schedstat_inc(rq->sched_goidle);
-
-	return rq->idle;
-}
-
-/*
- * It is not legal to sleep in the idle task - print a warning
- * message if some code attempts to do it:
- */
-static void
-dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
-{
-	raw_spin_unlock_irq(&rq->lock);
-	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
-	dump_stack();
-	raw_spin_lock_irq(&rq->lock);
-}
-
-static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
-{
-}
-
-/*
- * scheduler tick hitting a task of our scheduling class.
- *
- * NOTE: This function can be called remotely by the tick offload that
- * goes along full dynticks. Therefore no local assumption can be made
- * and everything must be accessed through the @rq and @curr passed in
- * parameters.
- */
-static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
-{
-}
-
-static void set_curr_task_idle(struct rq *rq)
-{
-}
-
-static void switched_to_idle(struct rq *rq, struct task_struct *p)
-{
-	BUG();
-}
-
-static void
-prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
-{
-	BUG();
-}
-
-static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
-{
-	return 0;
-}
-
-static void update_curr_idle(struct rq *rq)
-{
-}
-
-/*
- * Simple, special scheduling class for the per-CPU idle tasks:
- */
-const struct sched_class idle_sched_class = {
-	/* .next is NULL */
-	/* no enqueue/yield_task for idle tasks */
-
-	/* dequeue is not valid, we print a debug message there: */
-	.dequeue_task		= dequeue_task_idle,
-
-	.check_preempt_curr	= check_preempt_curr_idle,
-
-	.pick_next_task		= pick_next_task_idle,
-	.put_prev_task		= put_prev_task_idle,
-
-#ifdef CONFIG_SMP
-	.select_task_rq		= select_task_rq_idle,
-	.set_cpus_allowed	= set_cpus_allowed_common,
-#endif
-
-	.set_curr_task          = set_curr_task_idle,
-	.task_tick		= task_tick_idle,
-
-	.get_rr_interval	= get_rr_interval_idle,
-
-	.prio_changed		= prio_changed_idle,
-	.switched_to		= switched_to_idle,
-	.update_curr		= update_curr_idle,
-};