[PATCH v2 02/12] sched/isolation: Introduce housekeeping notifier infrastructure

[Qiliang Yuan <realwujing@gmail.com>]

Subsystems currently rely on static housekeeping masks determined at
boot. Supporting runtime reconfiguration (DHM v2) requires a mechanism
to broadcast mask changes to affected kernel components.

Implement a blocking notifier chain for housekeeping mask updates. This
infrastructure enables subsystems like genirq, workqueues, and RCU to
react dynamically to isolation changes triggered by cpusets.

Signed-off-by: Qiliang Yuan <realwujing@gmail.com>
---
 include/linux/sched/isolation.h | 21 +++++++++++++++++++++
 kernel/sched/isolation.c        | 26 ++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index b9a041247565c..aea1dbc4d7486 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -4,6 +4,7 @@
 #include <linux/cpumask.h>
 #include <linux/init.h>
 #include <linux/tick.h>
+#include <linux/notifier.h>
 
 enum hk_type {
 	/* Inverse of boot-time isolcpus= argument */
@@ -28,6 +29,13 @@ enum hk_type {
 
 #define HK_TYPE_KERNEL_NOISE HK_TYPE_TICK
 
+struct housekeeping_update {
+	enum hk_type type;
+	const struct cpumask *new_mask;
+};
+
+#define HK_UPDATE_MASK	0x01
+
 #ifdef CONFIG_CPU_ISOLATION
 DECLARE_STATIC_KEY_FALSE(housekeeping_overridden);
 extern int housekeeping_any_cpu(enum hk_type type);
@@ -38,6 +46,9 @@ extern bool housekeeping_test_cpu(int cpu, enum hk_type type);
 extern int housekeeping_update(struct cpumask *isol_mask);
 extern void __init housekeeping_init(void);
 
+extern int housekeeping_register_notifier(struct notifier_block *nb);
+extern int housekeeping_unregister_notifier(struct notifier_block *nb);
+
 #else
 
 static inline int housekeeping_any_cpu(enum hk_type type)
@@ -65,6 +76,16 @@ static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
 
 static inline int housekeeping_update(struct cpumask *isol_mask) { return 0; }
 static inline void housekeeping_init(void) { }
+
+static inline int housekeeping_register_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int housekeeping_unregister_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
 #endif /* CONFIG_CPU_ISOLATION */
 
 static inline bool housekeeping_cpu(int cpu, enum hk_type type)
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index e05ed5118e651..0462b41807161 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -10,6 +10,7 @@
 #include <linux/sched/isolation.h>
 #include <linux/pci.h>
 #include "sched.h"
+#include <linux/notifier.h>
 
 enum hk_flags {
 	HK_FLAG_DOMAIN_BOOT	= BIT(HK_TYPE_DOMAIN_BOOT),
@@ -26,6 +27,8 @@ enum hk_flags {
 #define HK_FLAG_KERNEL_NOISE (HK_FLAG_TICK | HK_FLAG_TIMER | HK_FLAG_RCU | \
 			      HK_FLAG_MISC | HK_FLAG_WQ | HK_FLAG_KTHREAD)
 
+static BLOCKING_NOTIFIER_HEAD(housekeeping_notifier_list);
+
 DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
 EXPORT_SYMBOL_GPL(housekeeping_overridden);
 
@@ -170,6 +173,29 @@ int housekeeping_update(struct cpumask *isol_mask)
 	return 0;
 }
 
+int housekeeping_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&housekeeping_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(housekeeping_register_notifier);
+
+int housekeeping_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&housekeeping_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(housekeeping_unregister_notifier);
+
+int housekeeping_update_notify(enum hk_type type, const struct cpumask *new_mask)
+{
+	struct housekeeping_update update = {
+		.type = type,
+		.new_mask = new_mask,
+	};
+
+	return blocking_notifier_call_chain(&housekeeping_notifier_list, HK_UPDATE_MASK, &update);
+}
+EXPORT_SYMBOL_GPL(housekeeping_update_notify);
+
 void __init housekeeping_init(void)
 {
 	enum hk_type type;

-- 
2.43.0