[tip: sched/urgent] sched: Provide idle_rq() helper

["tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>]

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

Commit-ID:     1e0a2ba7afb1b60f02599093d84b72ce62ad11c0
Gitweb:        https://git.kernel.org/tip/1e0a2ba7afb1b60f02599093d84b72ce62ad11c0
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Tue, 13 Jan 2026 10:50:41 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 13 Jan 2026 11:37:52 +01:00

sched: Provide idle_rq() helper

A fix for the dl_server 'requires' idle_cpu() usage, which made me
note that it and available_idle_cpu() are extern function calls.

And while idle_cpu() is used outside of kernel/sched/,
available_idle_cpu() is not.

This makes it hard to make idle_cpu() an inline helper, so provide
idle_rq() and implement idle_cpu() and available_idle_cpu() using
that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/sched.h   |  1 -
 kernel/sched/sched.h    | 22 ++++++++++++++++++++++
 kernel/sched/syscalls.c | 30 +-----------------------------
 3 files changed, 23 insertions(+), 30 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d395f28..da01335 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1874,7 +1874,6 @@ static inline int task_nice(const struct task_struct *p)
 extern int can_nice(const struct task_struct *p, const int nice);
 extern int task_curr(const struct task_struct *p);
 extern int idle_cpu(int cpu);
-extern int available_idle_cpu(int cpu);
 extern int sched_setscheduler(struct task_struct *, int, const struct sched_param *);
 extern int sched_setscheduler_nocheck(struct task_struct *, int, const struct sched_param *);
 extern void sched_set_fifo(struct task_struct *p);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d30cca6..e885a93 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1364,6 +1364,28 @@ static inline u32 sched_rng(void)
 #define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
 #define raw_rq()		raw_cpu_ptr(&runqueues)
 
+static inline bool idle_rq(struct rq *rq)
+{
+	return rq->curr == rq->idle && !rq->nr_running && !rq->ttwu_pending;
+}
+
+/**
+ * available_idle_cpu - is a given CPU idle for enqueuing work.
+ * @cpu: the CPU in question.
+ *
+ * Return: 1 if the CPU is currently idle. 0 otherwise.
+ */
+static inline bool available_idle_cpu(int cpu)
+{
+	if (!idle_rq(cpu_rq(cpu)))
+		return 0;
+
+	if (vcpu_is_preempted(cpu))
+		return 0;
+
+	return 1;
+}
+
 #ifdef CONFIG_SCHED_PROXY_EXEC
 static inline void rq_set_donor(struct rq *rq, struct task_struct *t)
 {
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index 0496dc2..cb337de 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -180,35 +180,7 @@ int task_prio(const struct task_struct *p)
  */
 int idle_cpu(int cpu)
 {
-	struct rq *rq = cpu_rq(cpu);
-
-	if (rq->curr != rq->idle)
-		return 0;
-
-	if (rq->nr_running)
-		return 0;
-
-	if (rq->ttwu_pending)
-		return 0;
-
-	return 1;
-}
-
-/**
- * available_idle_cpu - is a given CPU idle for enqueuing work.
- * @cpu: the CPU in question.
- *
- * Return: 1 if the CPU is currently idle. 0 otherwise.
- */
-int available_idle_cpu(int cpu)
-{
-	if (!idle_cpu(cpu))
-		return 0;
-
-	if (vcpu_is_preempted(cpu))
-		return 0;
-
-	return 1;
+	return idle_rq(cpu_rq(cpu));
 }
 
 /**