sched: Make const-safe

With a modified container_of() that preserves constness, the compiler
finds some pointers which should have been marked as const.  task_of()
also needs to become const-preserving for the !FAIR_GROUP_SCHED case so
that cfs_rq_of() can take a const argument.  No change to generated code.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221212144946.2657785-1-willy@infradead.org

kernel/sched/core.c

@@ -152,7 +152,7 @@ __read_mostly int scheduler_running;
 DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);
 
 /* kernel prio, less is more */
-static inline int __task_prio(struct task_struct *p)
+static inline int __task_prio(const struct task_struct *p)
 {
 	if (p->sched_class == &stop_sched_class) /* trumps deadline */
 		return -2;
@@ -174,7 +174,8 @@ static inline int __task_prio(struct task_struct *p)
  */
 
 /* real prio, less is less */
-static inline bool prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
+static inline bool prio_less(const struct task_struct *a,
+			     const struct task_struct *b, bool in_fi)
 {
 
 	int pa = __task_prio(a), pb = __task_prio(b);
@@ -194,7 +195,8 @@ static inline bool prio_less(struct task_struct *a, struct task_struct *b, bool
 	return false;
 }
 
-static inline bool __sched_core_less(struct task_struct *a, struct task_struct *b)
+static inline bool __sched_core_less(const struct task_struct *a,
+				     const struct task_struct *b)
 {
 	if (a->core_cookie < b->core_cookie)
 		return true;

kernel/sched/fair.c

@@ -468,7 +468,7 @@ is_same_group(struct sched_entity *se, struct sched_entity *pse)
 	return NULL;
 }
 
-static inline struct sched_entity *parent_entity(struct sched_entity *se)
+static inline struct sched_entity *parent_entity(const struct sched_entity *se)
 {
 	return se->parent;
 }
@@ -595,8 +595,8 @@ static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
 	return min_vruntime;
 }
 
-static inline bool entity_before(struct sched_entity *a,
-				struct sched_entity *b)
+static inline bool entity_before(const struct sched_entity *a,
+				 const struct sched_entity *b)
 {
 	return (s64)(a->vruntime - b->vruntime) < 0;
 }
@@ -11852,7 +11852,8 @@ static inline void task_tick_core(struct rq *rq, struct task_struct *curr)
 /*
  * se_fi_update - Update the cfs_rq->min_vruntime_fi in a CFS hierarchy if needed.
  */
-static void se_fi_update(struct sched_entity *se, unsigned int fi_seq, bool forceidle)
+static void se_fi_update(const struct sched_entity *se, unsigned int fi_seq,
+			 bool forceidle)
 {
 	for_each_sched_entity(se) {
 		struct cfs_rq *cfs_rq = cfs_rq_of(se);
@@ -11877,11 +11878,12 @@ void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi)
 	se_fi_update(se, rq->core->core_forceidle_seq, in_fi);
 }
 
-bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
+bool cfs_prio_less(const struct task_struct *a, const struct task_struct *b,
+			bool in_fi)
 {
 	struct rq *rq = task_rq(a);
-	struct sched_entity *sea = &a->se;
-	struct sched_entity *seb = &b->se;
+	const struct sched_entity *sea = &a->se;
+	const struct sched_entity *seb = &b->se;
 	struct cfs_rq *cfs_rqa;
 	struct cfs_rq *cfs_rqb;
 	s64 delta;

kernel/sched/sched.h

@@ -248,7 +248,7 @@ static inline void update_avg(u64 *avg, u64 sample)
 
 #define SCHED_DL_FLAGS (SCHED_FLAG_RECLAIM | SCHED_FLAG_DL_OVERRUN | SCHED_FLAG_SUGOV)
 
-static inline bool dl_entity_is_special(struct sched_dl_entity *dl_se)
+static inline bool dl_entity_is_special(const struct sched_dl_entity *dl_se)
 {
 #ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
 	return unlikely(dl_se->flags & SCHED_FLAG_SUGOV);
@@ -260,8 +260,8 @@ static inline bool dl_entity_is_special(struct sched_dl_entity *dl_se)
 /*
  * Tells if entity @a should preempt entity @b.
  */
-static inline bool
-dl_entity_preempt(struct sched_dl_entity *a, struct sched_dl_entity *b)
+static inline bool dl_entity_preempt(const struct sched_dl_entity *a,
+				     const struct sched_dl_entity *b)
 {
 	return dl_entity_is_special(a) ||
 	       dl_time_before(a->deadline, b->deadline);
@@ -1244,7 +1244,8 @@ static inline raw_spinlock_t *__rq_lockp(struct rq *rq)
 	return &rq->__lock;
 }
 
-bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool fi);
+bool cfs_prio_less(const struct task_struct *a, const struct task_struct *b,
+			bool fi);
 
 /*
  * Helpers to check if the CPU's core cookie matches with the task's cookie
@@ -1423,7 +1424,7 @@ static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
 }
 
 /* runqueue on which this entity is (to be) queued */
-static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
+static inline struct cfs_rq *cfs_rq_of(const struct sched_entity *se)
 {
 	return se->cfs_rq;
 }
@@ -1436,19 +1437,16 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
 
 #else
 
-static inline struct task_struct *task_of(struct sched_entity *se)
-{
-	return container_of(se, struct task_struct, se);
-}
+#define task_of(_se)	container_of(_se, struct task_struct, se)
 
-static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
+static inline struct cfs_rq *task_cfs_rq(const struct task_struct *p)
 {
 	return &task_rq(p)->cfs;
 }
 
-static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
+static inline struct cfs_rq *cfs_rq_of(const struct sched_entity *se)
 {
-	struct task_struct *p = task_of(se);
+	const struct task_struct *p = task_of(se);
 	struct rq *rq = task_rq(p);
 
 	return &rq->cfs;