[PATCH RFC 01/12] sched/isolation: Remove __init restriction from housekeeping cores

[Qiliang Yuan <realwujing@gmail.com>]

The current housekeeping management logic in kernel/sched/isolation.c is
heavily tied to the boot process. Functions like housekeeping_setup()
and housekeeping_init() are marked with __init, and they use
alloc_bootmem_cpumask_var() for memory allocation. This prevents any
runtime reconfiguration of housekeeping masks.

Refactor the infrastructure to support dynamic updates:
1. Remove __init markers from core functions to keep them available
   after boot.
2. Replace bootmem allocation with runtime-safe alloc_cpumask_var()
   using appropriate GFP flags (GFP_NOWAIT during early boot,
   GFP_KERNEL at runtime).
3. Introduce housekeeping_mutex to protect the global state during
   concurrent updates.
4. Update include/linux/sched/isolation.h to reflect function
   signature changes.

This lays the foundation for runtime isolation reconfiguration without
requiring a system reboot.

Signed-off-by: Qiliang Yuan <realwujing@gmail.com>
Signed-off-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
---
 include/linux/sched/isolation.h |  2 +-
 kernel/sched/isolation.c        | 32 ++++++++++++++++++++++++--------
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index d8501f4709b5..cecb80b09120 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -31,7 +31,7 @@ extern const struct cpumask *housekeeping_cpumask(enum hk_type type);
 extern bool housekeeping_enabled(enum hk_type type);
 extern void housekeeping_affine(struct task_struct *t, enum hk_type type);
 extern bool housekeeping_test_cpu(int cpu, enum hk_type type);
-extern void __init housekeeping_init(void);
+extern void housekeeping_init(void);
 
 #else
 
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 3ad0d6df6a0a..811bf6cbe68d 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -8,6 +8,7 @@
  *
  */
 #include <linux/sched/isolation.h>
+#include <linux/mutex.h>
 #include "sched.h"
 
 enum hk_flags {
@@ -16,6 +17,7 @@ enum hk_flags {
 	HK_FLAG_KERNEL_NOISE	= BIT(HK_TYPE_KERNEL_NOISE),
 };
 
+static DEFINE_MUTEX(housekeeping_mutex);
 DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
 EXPORT_SYMBOL_GPL(housekeeping_overridden);
 
@@ -84,7 +86,7 @@ bool housekeeping_test_cpu(int cpu, enum hk_type type)
 }
 EXPORT_SYMBOL_GPL(housekeeping_test_cpu);
 
-void __init housekeeping_init(void)
+void housekeeping_init(void)
 {
 	enum hk_type type;
 
@@ -102,20 +104,30 @@ void __init housekeeping_init(void)
 	}
 }
 
-static void __init housekeeping_setup_type(enum hk_type type,
+static void housekeeping_setup_type(enum hk_type type,
 					   cpumask_var_t housekeeping_staging)
 {
+	unsigned int gfp = GFP_KERNEL;
+
+	if (system_state < SYSTEM_RUNNING)
+		gfp = GFP_NOWAIT;
+
+	if (!housekeeping.cpumasks[type])
+		alloc_cpumask_var(&housekeeping.cpumasks[type], gfp);
 
-	alloc_bootmem_cpumask_var(&housekeeping.cpumasks[type]);
 	cpumask_copy(housekeeping.cpumasks[type],
 		     housekeeping_staging);
 }
 
-static int __init housekeeping_setup(char *str, unsigned long flags)
+static int housekeeping_setup(char *str, unsigned long flags)
 {
 	cpumask_var_t non_housekeeping_mask, housekeeping_staging;
 	unsigned int first_cpu;
 	int err = 0;
+	unsigned int gfp = GFP_KERNEL;
+
+	if (system_state < SYSTEM_RUNNING)
+		gfp = GFP_NOWAIT;
 
 	if ((flags & HK_FLAG_KERNEL_NOISE) && !(housekeeping.flags & HK_FLAG_KERNEL_NOISE)) {
 		if (!IS_ENABLED(CONFIG_NO_HZ_FULL)) {
@@ -125,13 +137,17 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
 		}
 	}
 
-	alloc_bootmem_cpumask_var(&non_housekeeping_mask);
+	if (!alloc_cpumask_var(&non_housekeeping_mask, gfp))
+		return 0;
+
 	if (cpulist_parse(str, non_housekeeping_mask) < 0) {
 		pr_warn("Housekeeping: nohz_full= or isolcpus= incorrect CPU range\n");
 		goto free_non_housekeeping_mask;
 	}
 
-	alloc_bootmem_cpumask_var(&housekeeping_staging);
+	if (!alloc_cpumask_var(&housekeeping_staging, gfp))
+		goto free_non_housekeeping_mask;
+
 	cpumask_andnot(housekeeping_staging,
 		       cpu_possible_mask, non_housekeeping_mask);
 
@@ -203,9 +219,9 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
 	err = 1;
 
 free_housekeeping_staging:
-	free_bootmem_cpumask_var(housekeeping_staging);
+	free_cpumask_var(housekeeping_staging);
 free_non_housekeeping_mask:
-	free_bootmem_cpumask_var(non_housekeeping_mask);
+	free_cpumask_var(non_housekeeping_mask);
 
 	return err;
 }

-- 
2.51.0