linux-kernel - [tip: sched/core] sched: Cleanup sched_delayed handling for class switches

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Message-ID: <176060721531.709179.10648552165493064488.tip-bot2@tip-bot2>
Date: Thu, 16 Oct 2025 09:33:35 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Juri Lelli <juri.lelli@...hat.com>, Tejun Heo <tj@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: sched/core] sched: Cleanup sched_delayed handling for class switches

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     1ae5f5dfe5adc64a90b1b0ab5bd9bd7c9d140c28
Gitweb:        https://git.kernel.org/tip/1ae5f5dfe5adc64a90b1b0ab5bd9bd7c9d140c28
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 30 Oct 2024 15:47:46 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 16 Oct 2025 11:13:51 +02:00

sched: Cleanup sched_delayed handling for class switches

Use the new sched_class::switching_from() method to dequeue delayed
tasks before switching to another class.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Reviewed-by: Juri Lelli <juri.lelli@...hat.com>
Acked-by: Tejun Heo <tj@...nel.org>
---
 kernel/sched/core.c     | 12 ++++++++----
 kernel/sched/ext.c      |  6 ------
 kernel/sched/fair.c     |  7 +++++++
 kernel/sched/syscalls.c |  3 ---
 4 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4dbd206..bd2c551 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7366,9 +7366,6 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 	if (prev_class != next_class)
 		queue_flag |= DEQUEUE_CLASS;
 
-	if (prev_class != next_class && p->se.sched_delayed)
-		dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
-
 	scoped_guard (sched_change, p, queue_flag) {
 		/*
 		 * Boosting condition are:
@@ -10840,8 +10837,15 @@ struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int 
 	lockdep_assert_rq_held(rq);
 
 	if (flags & DEQUEUE_CLASS) {
-		if (p->sched_class->switching_from)
+		if (p->sched_class->switching_from) {
+			/*
+			 * switching_from_fair() assumes CLASS implies NOCLOCK;
+			 * fixing this assumption would mean switching_from()
+			 * would need to be able to change flags.
+			 */
+			WARN_ON(!(flags & DEQUEUE_NOCLOCK));
 			p->sched_class->switching_from(rq, p);
+		}
 	}
 
 	*ctx = (struct sched_change_ctx){
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index a408c39..b0a1e2a 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3922,9 +3922,6 @@ static void scx_disable_workfn(struct kthread_work *work)
 		if (old_class != new_class)
 			queue_flags |= DEQUEUE_CLASS;
 
-		if (old_class != new_class && p->se.sched_delayed)
-			dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
-
 		scoped_guard (sched_change, p, queue_flags) {
 			p->sched_class = new_class;
 		}
@@ -4673,9 +4670,6 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
 		if (old_class != new_class)
 			queue_flags |= DEQUEUE_CLASS;
 
-		if (old_class != new_class && p->se.sched_delayed)
-			dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
-
 		scoped_guard (sched_change, p, queue_flags) {
 			p->scx.slice = SCX_SLICE_DFL;
 			p->sched_class = new_class;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ac881df..6c462e4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -13249,6 +13249,12 @@ static void attach_task_cfs_rq(struct task_struct *p)
 	attach_entity_cfs_rq(se);
 }
 
+static void switching_from_fair(struct rq *rq, struct task_struct *p)
+{
+	if (p->se.sched_delayed)
+		dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
+}
+
 static void switched_from_fair(struct rq *rq, struct task_struct *p)
 {
 	detach_task_cfs_rq(p);
@@ -13650,6 +13656,7 @@ DEFINE_SCHED_CLASS(fair) = {
 
 	.reweight_task		= reweight_task_fair,
 	.prio_changed		= prio_changed_fair,
+	.switching_from		= switching_from_fair,
 	.switched_from		= switched_from_fair,
 	.switched_to		= switched_to_fair,
 
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index bcef5c7..6583faf 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -687,9 +687,6 @@ change:
 	if (prev_class != next_class)
 		queue_flags |= DEQUEUE_CLASS;
 
-	if (prev_class != next_class && p->se.sched_delayed)
-		dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
-
 	scoped_guard (sched_change, p, queue_flags) {
 
 		if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {