Message-ID: <20251013203146.10162-14-frederic@kernel.org>
Date: Mon, 13 Oct 2025 22:31:26 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
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Subject: [PATCH 13/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset

Until now, HK_TYPE_DOMAIN used to only include boot defined isolated
CPUs passed through isolcpus= boot option. Users interested in also
knowing the runtime defined isolated CPUs through cpuset must use
different APIs: cpuset_cpu_is_isolated(), cpu_is_isolated(), etc...

There are many drawbacks to that approach:

1) Most interested subsystems want to know about all isolated CPUs, not
  just those defined on boot time.

2) cpuset_cpu_is_isolated() / cpu_is_isolated() are not synchronized with
  concurrent cpuset changes.

3) Further cpuset modifications are not propagated to subsystems

Solve 1) and 2) and centralize all isolated CPUs within the
HK_TYPE_DOMAIN housekeeping cpumask.

Subsystems can rely on RCU to synchronize against concurrent changes.

The propagation mentioned in 3) will be handled in further patches.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 include/linux/sched/isolation.h |  2 +
 kernel/cgroup/cpuset.c          |  2 +
 kernel/sched/isolation.c        | 75 ++++++++++++++++++++++++++++++---
 kernel/sched/sched.h            |  1 +
 4 files changed, 74 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index da22b038942a..94d5c835121b 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -32,6 +32,7 @@ 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 int housekeeping_update(struct cpumask *mask, enum hk_type type);
 extern void __init housekeeping_init(void);
 
 #else
@@ -59,6 +60,7 @@ static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
 	return true;
 }
 
+static inline int housekeeping_update(struct cpumask *mask, enum hk_type type) { return 0; }
 static inline void housekeeping_init(void) { }
 #endif /* CONFIG_CPU_ISOLATION */
 
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index aa1ac7bcf2ea..b04a4242f2fa 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1403,6 +1403,8 @@ static void update_unbound_workqueue_cpumask(bool isolcpus_updated)
 
 	ret = workqueue_unbound_exclude_cpumask(isolated_cpus);
 	WARN_ON_ONCE(ret < 0);
+	ret = housekeeping_update(isolated_cpus, HK_TYPE_DOMAIN);
+	WARN_ON_ONCE(ret < 0);
 }
 
 /**
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index b46c20b5437f..95d69c2102f6 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -29,18 +29,48 @@ static struct housekeeping housekeeping;
 
 bool housekeeping_enabled(enum hk_type type)
 {
-	return !!(housekeeping.flags & BIT(type));
+	return !!(READ_ONCE(housekeeping.flags) & BIT(type));
 }
 EXPORT_SYMBOL_GPL(housekeeping_enabled);
 
+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;
+
+		/* 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 lock held, partitions not writable */
+		if (IS_ENABLED(CONFIG_CPUSETS) && lockdep_is_cpuset_held())
+			return true;
+
+		return false;
+	}
+
+	return true;
+}
+
+static inline struct cpumask *housekeeping_cpumask_dereference(enum hk_type type)
+{
+	return rcu_dereference_check(housekeeping.cpumasks[type],
+				     housekeeping_dereference_check(type));
+}
+
 const struct cpumask *housekeeping_cpumask(enum hk_type type)
 {
+	const struct cpumask *mask = NULL;
+
 	if (static_branch_unlikely(&housekeeping_overridden)) {
-		if (housekeeping.flags & BIT(type)) {
-			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
-		}
+		if (READ_ONCE(housekeeping.flags) & BIT(type))
+			mask = housekeeping_cpumask_dereference(type);
 	}
-	return cpu_possible_mask;
+	if (!mask)
+		mask = cpu_possible_mask;
+	return mask;
 }
 EXPORT_SYMBOL_GPL(housekeeping_cpumask);
 
@@ -80,12 +110,45 @@ EXPORT_SYMBOL_GPL(housekeeping_affine);
 
 bool housekeeping_test_cpu(int cpu, enum hk_type type)
 {
-	if (housekeeping.flags & BIT(type))
+	if (READ_ONCE(housekeeping.flags) & BIT(type))
 		return cpumask_test_cpu(cpu, housekeeping_cpumask(type));
 	return true;
 }
 EXPORT_SYMBOL_GPL(housekeeping_test_cpu);
 
+int housekeeping_update(struct cpumask *mask, enum hk_type type)
+{
+	struct cpumask *trial, *old = NULL;
+
+	if (type != HK_TYPE_DOMAIN)
+		return -ENOTSUPP;
+
+	trial = kmalloc(sizeof(*trial), GFP_KERNEL);
+	if (!trial)
+		return -ENOMEM;
+
+	cpumask_andnot(trial, housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT), mask);
+	if (!cpumask_intersects(trial, cpu_online_mask)) {
+		kfree(trial);
+		return -EINVAL;
+	}
+
+	if (!housekeeping.flags)
+		static_branch_enable(&housekeeping_overridden);
+
+	if (!(housekeeping.flags & BIT(type)))
+		old = housekeeping_cpumask_dereference(type);
+	else
+		WRITE_ONCE(housekeeping.flags, housekeeping.flags | BIT(type));
+	rcu_assign_pointer(housekeeping.cpumasks[type], trial);
+
+	synchronize_rcu();
+
+	kfree(old);
+
+	return 0;
+}
+
 void __init housekeeping_init(void)
 {
 	enum hk_type type;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0c0ef8999fd6..8fac8aa451c6 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -30,6 +30,7 @@
 #include <linux/context_tracking.h>
 #include <linux/cpufreq.h>
 #include <linux/cpumask_api.h>
+#include <linux/cpuset.h>
 #include <linux/ctype.h>
 #include <linux/file.h>
 #include <linux/fs_api.h>
-- 
2.51.0

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