[PATCH 05/18] sched: Pass next class to sched_change_begin()

[Andrea Righi <arighi@nvidia.com>]

sched_change_begin() currently only receives the task whose scheduling
state is being changed. It cannot distinguish a class transition from a
same-class update before recording the task queueing state.

Pass the incoming scheduling class to sched_change_begin() and update all
callers. This allows transition handling to run before the normal dequeue
and class change.

This is a preparatory change to support proxy execution with sched_ext.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
 kernel/sched/core.c     | 12 +++++++-----
 kernel/sched/ext/ext.c  |  7 ++++---
 kernel/sched/ext/sub.c  |  9 ++++++---
 kernel/sched/sched.h    |  9 ++++++---
 kernel/sched/syscalls.c |  4 ++--
 5 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0a2eabadfee02..26b8da8c8a2c5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2802,7 +2802,7 @@ void set_cpus_allowed_common(struct task_struct *p, struct affinity_context *ctx
 static void
 do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
 {
-	scoped_guard (sched_change, p, DEQUEUE_SAVE)
+	scoped_guard (sched_change, p, p->sched_class, DEQUEUE_SAVE)
 		p->sched_class->set_cpus_allowed(p, ctx);
 }
 
@@ -7753,7 +7753,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 	if (prev_class != next_class)
 		queue_flag |= DEQUEUE_CLASS;
 
-	scoped_guard (sched_change, p, queue_flag) {
+	scoped_guard (sched_change, p, next_class, queue_flag) {
 		/*
 		 * Boosting condition are:
 		 * 1. -rt task is running and holds mutex A
@@ -8430,7 +8430,7 @@ int migrate_task_to(struct task_struct *p, int target_cpu)
 void sched_setnuma(struct task_struct *p, int nid)
 {
 	guard(task_rq_lock)(p);
-	scoped_guard (sched_change, p, DEQUEUE_SAVE)
+	scoped_guard (sched_change, p, p->sched_class, DEQUEUE_SAVE)
 		p->numa_preferred_nid = nid;
 }
 #endif /* CONFIG_NUMA_BALANCING */
@@ -9548,7 +9548,7 @@ void sched_move_task(struct task_struct *tsk, bool for_autogroup)
 	CLASS(task_rq_lock, rq_guard)(tsk);
 	rq = rq_guard.rq;
 
-	scoped_guard (sched_change, tsk, queue_flags) {
+	scoped_guard (sched_change, tsk, tsk->sched_class, queue_flags) {
 		sched_change_group(tsk);
 		if (!for_autogroup)
 			scx_cgroup_move_task(tsk);
@@ -11252,7 +11252,9 @@ static inline void sched_mm_cid_fork(struct task_struct *t) { }
 
 static DEFINE_PER_CPU(struct sched_change_ctx, sched_change_ctx);
 
-struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int flags)
+struct sched_change_ctx *
+sched_change_begin(struct task_struct *p, const struct sched_class *next_class,
+		   unsigned int flags)
 {
 	struct sched_change_ctx *ctx = this_cpu_ptr(&sched_change_ctx);
 	struct rq *rq = task_rq(p);
diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 10af28a9f2c0c..00c368e2fc82d 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -6159,7 +6159,8 @@ void scx_bypass(struct scx_sched *sch, bool bypass)
 				scx_task_slice_ended(rq, p);
 
 			/* cycling deq/enq is enough, see the function comment */
-			scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+			scoped_guard (sched_change, p, p->sched_class,
+				      DEQUEUE_SAVE | DEQUEUE_MOVE) {
 				/* nothing */ ;
 			}
 		}
@@ -6441,7 +6442,7 @@ static void scx_root_disable(struct scx_sched *sch)
 		if (old_class != new_class)
 			queue_flags |= DEQUEUE_CLASS;
 
-		scoped_guard (sched_change, p, queue_flags) {
+		scoped_guard (sched_change, p, new_class, queue_flags) {
 			p->sched_class = new_class;
 		}
 
@@ -7802,7 +7803,7 @@ static void scx_root_enable_workfn(struct kthread_work *work)
 		if (old_class != new_class)
 			queue_flags |= DEQUEUE_CLASS;
 
-		scoped_guard (sched_change, p, queue_flags) {
+		scoped_guard (sched_change, p, new_class, queue_flags) {
 			scx_set_task_slice(p, READ_ONCE(sch->slice_dfl));
 			p->sched_class = new_class;
 		}
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
index 0554448835bd0..c3955c8163a03 100644
--- a/kernel/sched/ext/sub.c
+++ b/kernel/sched/ext/sub.c
@@ -1255,7 +1255,8 @@ static void scx_rehome_task(struct scx_sched *to, struct task_struct *p)
 	lockdep_assert_held(&p->pi_lock);
 	lockdep_assert_rq_held(task_rq(p));
 
-	scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+	scoped_guard (sched_change, p, p->sched_class,
+		      DEQUEUE_SAVE | DEQUEUE_MOVE) {
 		scx_disable_and_exit_task(scx_task_sched(p), p);
 		scx_set_task_state(p, SCX_TASK_INIT_BEGIN);
 		scx_set_task_state(p, SCX_TASK_INIT);
@@ -1285,7 +1286,8 @@ static void scx_punt_task(struct scx_sched *to, struct task_struct *p)
 	lockdep_assert_rq_held(task_rq(p));
 	WARN_ON_ONCE(!READ_ONCE(to->bypass_depth));
 
-	scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+	scoped_guard (sched_change, p, p->sched_class,
+		      DEQUEUE_SAVE | DEQUEUE_MOVE) {
 		scx_disable_and_exit_task(scx_task_sched(p), p);
 		scx_set_task_sched(p, to);
 	}
@@ -1939,7 +1941,8 @@ void scx_sub_enable_workfn(struct kthread_work *work)
 		if (!(p->scx.flags & SCX_TASK_SUB_INIT))
 			continue;
 
-		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+		scoped_guard (sched_change, p, p->sched_class,
+			      DEQUEUE_SAVE | DEQUEUE_MOVE) {
 			/*
 			 * $p must be either READY or ENABLED. If ENABLED,
 			 * __scx_disabled_and_exit_task() first disables and
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e656c7059bf86..6bba1f3b5d4cd 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -4240,13 +4240,16 @@ struct sched_change_ctx {
 	bool			running;
 };
 
-struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int flags);
+struct sched_change_ctx *
+sched_change_begin(struct task_struct *p, const struct sched_class *next_class,
+		   unsigned int flags);
 void sched_change_end(struct sched_change_ctx *ctx);
 
 DEFINE_CLASS(sched_change, struct sched_change_ctx *,
 	     sched_change_end(_T),
-	     sched_change_begin(p, flags),
-	     struct task_struct *p, unsigned int flags)
+	     sched_change_begin(p, next_class, flags),
+	     struct task_struct *p, const struct sched_class *next_class,
+	     unsigned int flags)
 
 DEFINE_CLASS_IS_UNCONDITIONAL(sched_change)
 
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index b215b0ead9a60..bc32ce76ff4fe 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -85,7 +85,7 @@ void set_user_nice(struct task_struct *p, long nice)
 		return;
 	}
 
-	scoped_guard (sched_change, p, DEQUEUE_SAVE) {
+	scoped_guard (sched_change, p, p->sched_class, DEQUEUE_SAVE) {
 		p->static_prio = NICE_TO_PRIO(nice);
 		set_load_weight(p, true);
 		old_prio = p->prio;
@@ -678,7 +678,7 @@ int __sched_setscheduler(struct task_struct *p,
 	if (prev_class != next_class)
 		queue_flags |= DEQUEUE_CLASS;
 
-	scoped_guard (sched_change, p, queue_flags) {
+	scoped_guard (sched_change, p, next_class, queue_flags) {
 
 		if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {
 			__setscheduler_params(p, attr);
-- 
2.55.0