[PATCH v3 03/13] sched/isolation: RCU-protect all housekeeping cpumask readers

[Jing Wu]

Extend housekeeping_dereference_check() to validate all runtime-mutable
types (HK_TYPE_DOMAIN, HK_TYPE_KERNEL_NOISE, HK_TYPE_MANAGED_IRQ), not
only HK_TYPE_DOMAIN.  Boot-only types (HK_TYPE_DOMAIN_BOOT) remain
unchecked.

Add housekeeping_cpumask_rcu() for callers that already hold an RCU
read lock.  This variant uses rcu_dereference() without the lockdep
annotation, avoiding false-positive lockdep warnings in RCU read-side
critical sections.

Use READ_ONCE() consistently when testing housekeeping.flags in paths
that may race with housekeeping_update_types().

Signed-off-by: Jing Wu <realwujing@xxxxxxxxx>
Signed-off-by: Qiliang Yuan <yuanql9@xxxxxxxxxxxxxxx>
---
 include/linux/sched/isolation.h |  6 +++++
 kernel/sched/isolation.c        | 57 +++++++++++++++++++++++++++++++----------
 2 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index eecbcbe802bd0..ed6e1c6980131 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -40,6 +40,7 @@ enum hk_type {
 DECLARE_STATIC_KEY_FALSE(housekeeping_overridden);
 extern int housekeeping_any_cpu(enum hk_type type);
 extern const struct cpumask *housekeeping_cpumask(enum hk_type type);
+extern const struct cpumask *housekeeping_cpumask_rcu(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);
@@ -87,6 +88,11 @@ static inline const struct cpumask *housekeeping_cpumask(enum hk_type type)
 	return cpu_possible_mask;
 }
 
+static inline const struct cpumask *housekeeping_cpumask_rcu(enum hk_type type)
+{
+	return cpu_possible_mask;
+}
+
 static inline bool housekeeping_enabled(enum hk_type type)
 {
 	return false;
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 4eca18cc5e8ce..3d5d3f12853c7 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -121,25 +121,40 @@ bool housekeeping_enabled(enum hk_type type)
 }
 EXPORT_SYMBOL_GPL(housekeeping_enabled);
 
+/*
+ * Types that can change at runtime via cpuset isolated partitions.
+ * Boot-only types (DOMAIN_BOOT) are always safe to read without lockdep.
+ */
+static bool housekeeping_type_can_change(enum hk_type type)
+{
+	switch (type) {
+	case HK_TYPE_DOMAIN:
+	case HK_TYPE_KERNEL_NOISE:
+	case HK_TYPE_MANAGED_IRQ:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static bool housekeeping_dereference_check(enum hk_type type)
 {
-	if (IS_ENABLED(CONFIG_LOCKDEP) && type == HK_TYPE_DOMAIN) {
-		/* Cpuset isn't even writable yet? */
-		if (system_state <= SYSTEM_SCHEDULING)
-			return true;
+	if (!IS_ENABLED(CONFIG_LOCKDEP) || !housekeeping_type_can_change(type))
+		return true;
 
-		/* CPU hotplug write locked, so cpuset partition can't be overwritten */
-		if (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_write_held())
-			return true;
+	/* Cpuset isn't even writable yet? */
+	if (system_state <= SYSTEM_SCHEDULING)
+		return true;
 
-		/* Cpuset lock held, partitions not writable */
-		if (IS_ENABLED(CONFIG_CPUSETS) && lockdep_is_cpuset_held())
-			return true;
+	/* CPU hotplug write locked, so cpuset partition can't be overwritten */
+	if (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_write_held())
+		return true;
 
-		return false;
-	}
+	/* Cpuset lock held, partitions not writable */
+	if (IS_ENABLED(CONFIG_CPUSETS) && lockdep_is_cpuset_held())
+		return true;
 
-	return true;
+	return false;
 }
 
 static inline struct cpumask *housekeeping_cpumask_dereference(enum hk_type type)
@@ -162,12 +177,26 @@ const struct cpumask *housekeeping_cpumask(enum hk_type type)
 }
 EXPORT_SYMBOL_GPL(housekeeping_cpumask);
 
+const struct cpumask *housekeeping_cpumask_rcu(enum hk_type type)
+{
+	const struct cpumask *mask = NULL;
+
+	if (static_branch_unlikely(&housekeeping_overridden)) {
+		if (READ_ONCE(housekeeping.flags) & BIT(type))
+			mask = rcu_dereference(housekeeping.cpumasks[type]);
+	}
+	if (!mask)
+		mask = cpu_possible_mask;
+	return mask;
+}
+EXPORT_SYMBOL_GPL(housekeeping_cpumask_rcu);
+
 int housekeeping_any_cpu(enum hk_type type)
 {
 	int cpu;
 
 	if (static_branch_unlikely(&housekeeping_overridden)) {
-		if (housekeeping.flags & BIT(type)) {
+		if (READ_ONCE(housekeeping.flags) & BIT(type)) {
 			cpu = sched_numa_find_closest(housekeeping_cpumask(type), smp_processor_id());
 			if (cpu < nr_cpu_ids)
 				return cpu;

-- 
2.43.0