PM: EM: Address RCU-related sparse warnings

The usage of __rcu in the Energy Model code is quite inconsistent
which causes the following sparse warnings to trigger:

kernel/power/energy_model.c:169:15: warning: incorrect type in assignment (different address spaces)
kernel/power/energy_model.c:169:15:    expected struct em_perf_table [noderef] __rcu *table
kernel/power/energy_model.c:169:15:    got struct em_perf_table *
kernel/power/energy_model.c:171:9: warning: incorrect type in argument 1 (different address spaces)
kernel/power/energy_model.c:171:9:    expected struct callback_head *head
kernel/power/energy_model.c:171:9:    got struct callback_head [noderef] __rcu *
kernel/power/energy_model.c:171:9: warning: cast removes address space '__rcu' of expression
kernel/power/energy_model.c:182:19: warning: incorrect type in argument 1 (different address spaces)
kernel/power/energy_model.c:182:19:    expected struct kref *kref
kernel/power/energy_model.c:182:19:    got struct kref [noderef] __rcu *
kernel/power/energy_model.c:200:15: warning: incorrect type in assignment (different address spaces)
kernel/power/energy_model.c:200:15:    expected struct em_perf_table [noderef] __rcu *table
kernel/power/energy_model.c:200:15:    got void *[assigned] _res
kernel/power/energy_model.c:204:20: warning: incorrect type in argument 1 (different address spaces)
kernel/power/energy_model.c:204:20:    expected struct kref *kref
kernel/power/energy_model.c:204:20:    got struct kref [noderef] __rcu *
kernel/power/energy_model.c:320:19: warning: incorrect type in argument 1 (different address spaces)
kernel/power/energy_model.c:320:19:    expected struct kref *kref
kernel/power/energy_model.c:320:19:    got struct kref [noderef] __rcu *
kernel/power/energy_model.c:325:45: warning: incorrect type in argument 2 (different address spaces)
kernel/power/energy_model.c:325:45:    expected struct em_perf_state *table
kernel/power/energy_model.c:325:45:    got struct em_perf_state [noderef] __rcu *
kernel/power/energy_model.c:425:45: warning: incorrect type in argument 3 (different address spaces)
kernel/power/energy_model.c:425:45:    expected struct em_perf_state *table
kernel/power/energy_model.c:425:45:    got struct em_perf_state [noderef] __rcu *
kernel/power/energy_model.c:442:15: warning: incorrect type in argument 1 (different address spaces)
kernel/power/energy_model.c:442:15:    expected void const *objp
kernel/power/energy_model.c:442:15:    got struct em_perf_table [noderef] __rcu *[assigned] em_table
kernel/power/energy_model.c:626:55: warning: incorrect type in argument 2 (different address spaces)
kernel/power/energy_model.c:626:55:    expected struct em_perf_state *table
kernel/power/energy_model.c:626:55:    got struct em_perf_state [noderef] __rcu *
kernel/power/energy_model.c:681:16: warning: incorrect type in assignment (different address spaces)
kernel/power/energy_model.c:681:16:    expected struct em_perf_state *new_ps
kernel/power/energy_model.c:681:16:    got struct em_perf_state [noderef] __rcu *
kernel/power/energy_model.c:699:37: warning: incorrect type in argument 2 (different address spaces)
kernel/power/energy_model.c:699:37:    expected struct em_perf_state *table
kernel/power/energy_model.c:699:37:    got struct em_perf_state [noderef] __rcu *
kernel/power/energy_model.c:733:38: warning: incorrect type in argument 3 (different address spaces)
kernel/power/energy_model.c:733:38:    expected struct em_perf_state *table
kernel/power/energy_model.c:733:38:    got struct em_perf_state [noderef] __rcu *
kernel/power/energy_model.c:855:53: warning: dereference of noderef expression
kernel/power/energy_model.c:864:32: warning: dereference of noderef expression

This is because the __rcu annotation for sparse is only applicable to
pointers that need rcu_dereference() or equivalent for protection, which
basically means pointers assigned with rcu_assign_pointer().

Make all of the above sparse warnings go away by cleaning up the usage
of __rcu and using rcu_dereference_protected() where applicable.

Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/5885405.DvuYhMxLoT@rjwysocki.net

Author: rafaeljw

include/linux/energy_model.h

@@ -167,13 +167,13 @@ struct em_data_callback {
 struct em_perf_domain *em_cpu_get(int cpu);
 struct em_perf_domain *em_pd_get(struct device *dev);
 int em_dev_update_perf_domain(struct device *dev,
-			      struct em_perf_table __rcu *new_table);
+			      struct em_perf_table *new_table);
 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 				const struct em_data_callback *cb,
 				const cpumask_t *cpus, bool microwatts);
 void em_dev_unregister_perf_domain(struct device *dev);
-struct em_perf_table __rcu *em_table_alloc(struct em_perf_domain *pd);
-void em_table_free(struct em_perf_table __rcu *table);
+struct em_perf_table *em_table_alloc(struct em_perf_domain *pd);
+void em_table_free(struct em_perf_table *table);
 int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
 			 int nr_states);
 int em_dev_update_chip_binning(struct device *dev);
@@ -373,14 +373,14 @@ static inline int em_pd_nr_perf_states(struct em_perf_domain *pd)
 	return 0;
 }
 static inline
-struct em_perf_table __rcu *em_table_alloc(struct em_perf_domain *pd)
+struct em_perf_table *em_table_alloc(struct em_perf_domain *pd)
 {
 	return NULL;
 }
-static inline void em_table_free(struct em_perf_table __rcu *table) {}
+static inline void em_table_free(struct em_perf_table *table) {}
 static inline
 int em_dev_update_perf_domain(struct device *dev,
-			      struct em_perf_table __rcu *new_table)
+			      struct em_perf_table *new_table)
 {
 	return -EINVAL;
 }

kernel/power/energy_model.c

@@ -163,12 +163,8 @@ static void em_debug_remove_pd(struct device *dev) {}
 
 static void em_release_table_kref(struct kref *kref)
 {
-	struct em_perf_table __rcu *table;
-
 	/* It was the last owner of this table so we can free */
-	table = container_of(kref, struct em_perf_table, kref);
-
-	kfree_rcu(table, rcu);
+	kfree_rcu(container_of(kref, struct em_perf_table, kref), rcu);
 }
 
 /**
@@ -177,7 +173,7 @@ static void em_release_table_kref(struct kref *kref)
  *
  * No return values.
  */
-void em_table_free(struct em_perf_table __rcu *table)
+void em_table_free(struct em_perf_table *table)
 {
 	kref_put(&table->kref, em_release_table_kref);
 }
@@ -190,9 +186,9 @@ void em_table_free(struct em_perf_table __rcu *table)
  * has a user.
  * Returns allocated table or NULL.
  */
-struct em_perf_table __rcu *em_table_alloc(struct em_perf_domain *pd)
+struct em_perf_table *em_table_alloc(struct em_perf_domain *pd)
 {
-	struct em_perf_table __rcu *table;
+	struct em_perf_table *table;
 	int table_size;
 
 	table_size = sizeof(struct em_perf_state) * pd->nr_perf_states;
@@ -300,9 +296,9 @@ int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
  * Return 0 on success or an error code on failure.
  */
 int em_dev_update_perf_domain(struct device *dev,
-			      struct em_perf_table __rcu *new_table)
+			      struct em_perf_table *new_table)
 {
-	struct em_perf_table __rcu *old_table;
+	struct em_perf_table *old_table;
 	struct em_perf_domain *pd;
 
 	if (!dev)
@@ -319,7 +315,8 @@ int em_dev_update_perf_domain(struct device *dev,
 
 	kref_get(&new_table->kref);
 
-	old_table = pd->em_table;
+	old_table = rcu_dereference_protected(pd->em_table,
+					      lockdep_is_held(&em_pd_mutex));
 	rcu_assign_pointer(pd->em_table, new_table);
 
 	em_cpufreq_update_efficiencies(dev, new_table->state);
@@ -392,7 +389,7 @@ static int em_create_pd(struct device *dev, int nr_states,
 			const cpumask_t *cpus,
 			unsigned long flags)
 {
-	struct em_perf_table __rcu *em_table;
+	struct em_perf_table *em_table;
 	struct em_perf_domain *pd;
 	struct device *cpu_dev;
 	int cpu, ret, num_cpus;
@@ -552,6 +549,7 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 				const struct em_data_callback *cb,
 				const cpumask_t *cpus, bool microwatts)
 {
+	struct em_perf_table *em_table;
 	unsigned long cap, prev_cap = 0;
 	unsigned long flags = 0;
 	int cpu, ret;
@@ -624,7 +622,9 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 	dev->em_pd->min_perf_state = 0;
 	dev->em_pd->max_perf_state = nr_states - 1;
 
-	em_cpufreq_update_efficiencies(dev, dev->em_pd->em_table->state);
+	em_table = rcu_dereference_protected(dev->em_pd->em_table,
+					     lockdep_is_held(&em_pd_mutex));
+	em_cpufreq_update_efficiencies(dev, em_table->state);
 
 	em_debug_create_pd(dev);
 	dev_info(dev, "EM: created perf domain\n");
@@ -661,17 +661,18 @@ void em_dev_unregister_perf_domain(struct device *dev)
 	mutex_lock(&em_pd_mutex);
 	em_debug_remove_pd(dev);
 
-	em_table_free(dev->em_pd->em_table);
+	em_table_free(rcu_dereference_protected(dev->em_pd->em_table,
+						lockdep_is_held(&em_pd_mutex)));
 
 	kfree(dev->em_pd);
 	dev->em_pd = NULL;
 	mutex_unlock(&em_pd_mutex);
 }
 EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);
 
-static struct em_perf_table __rcu *em_table_dup(struct em_perf_domain *pd)
+static struct em_perf_table *em_table_dup(struct em_perf_domain *pd)
 {
-	struct em_perf_table __rcu *em_table;
+	struct em_perf_table *em_table;
 	struct em_perf_state *ps, *new_ps;
 	int ps_size;
 
@@ -693,7 +694,7 @@ static struct em_perf_table __rcu *em_table_dup(struct em_perf_domain *pd)
 }
 
 static int em_recalc_and_update(struct device *dev, struct em_perf_domain *pd,
-				struct em_perf_table __rcu *em_table)
+				struct em_perf_table *em_table)
 {
 	int ret;
 
@@ -723,7 +724,7 @@ static int em_recalc_and_update(struct device *dev, struct em_perf_domain *pd,
 static void em_adjust_new_capacity(struct device *dev,
 				   struct em_perf_domain *pd)
 {
-	struct em_perf_table __rcu *em_table;
+	struct em_perf_table *em_table;
 
 	em_table = em_table_dup(pd);
 	if (!em_table) {
@@ -814,7 +815,7 @@ static void em_update_workfn(struct work_struct *work)
  */
 int em_dev_update_chip_binning(struct device *dev)
 {
-	struct em_perf_table __rcu *em_table;
+	struct em_perf_table *em_table;
 	struct em_perf_domain *pd;
 	int i, ret;