From 2be4686d866ad5896f2bb94d82fe892197aea9c7 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@kernel.org>
Date: Fri, 27 Oct 2023 16:40:47 +0200
Subject: [PATCH] rcu: Introduce rcu_cpu_online()
Export the RCU point of view as to when a CPU is considered offline
(ie: when does RCU consider that a CPU is sufficiently down in the
hotplug process to not feature any possible read side).
This will be used by RCU-tasks whose vision of an offline CPU should
reasonably match the one of RCU core.
Fixes: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup")
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
kernel/rcu/rcu.h | 2 ++
kernel/rcu/tree.c | 7 +++++++
2 files changed, 9 insertions(+)
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 0d866eaa4cc86..b531c33e9545b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -500,6 +500,7 @@ static inline void rcu_expedite_gp(void) { }
static inline void rcu_unexpedite_gp(void) { }
static inline void rcu_async_hurry(void) { }
static inline void rcu_async_relax(void) { }
+static inline bool rcu_cpu_online(int cpu) { return true; }
#else /* #ifdef CONFIG_TINY_RCU */
bool rcu_gp_is_normal(void); /* Internal RCU use. */
bool rcu_gp_is_expedited(void); /* Internal RCU use. */
@@ -509,6 +510,7 @@ void rcu_unexpedite_gp(void);
void rcu_async_hurry(void);
void rcu_async_relax(void);
void rcupdate_announce_bootup_oddness(void);
+bool rcu_cpu_online(int cpu);
#ifdef CONFIG_TASKS_RCU_GENERIC
void show_rcu_tasks_gp_kthreads(void);
#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 77e7a0dc722aa..c3359f4c88307 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4216,6 +4216,13 @@ static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
}
+bool rcu_cpu_online(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ return rcu_rdp_cpu_online(rdp);
+}
+
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
/*
--
2.30.2