[PATCH 13/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset

Frederic Weisbecker
2025-10-13T20:33:41Z

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@kernel.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