HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
A synchronization mechanism is then needed to synchronize the updates
with the housekeeping cpumask readers.

Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
cpumask will be modified, the update side will wait for an RCU grace
period and propagate the change to interested subsystem when deemed
necessary.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
 kernel/sched/sched.h     |  1 +
 2 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 11a623fa6320..83be49ec2b06 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
 EXPORT_SYMBOL_GPL(housekeeping_overridden);
 
 struct housekeeping {
-	cpumask_var_t cpumasks[HK_TYPE_MAX];
+	struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
 	unsigned long flags;
 };
 
@@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
 }
 EXPORT_SYMBOL_GPL(housekeeping_enabled);
 
+const struct cpumask *housekeeping_cpumask(enum hk_type type)
+{
+	if (static_branch_unlikely(&housekeeping_overridden)) {
+		if (housekeeping.flags & BIT(type)) {
+			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
+		}
+	}
+	return cpu_possible_mask;
+}
+EXPORT_SYMBOL_GPL(housekeeping_cpumask);
+
 int housekeeping_any_cpu(enum hk_type type)
 {
 	int cpu;
 
 	if (static_branch_unlikely(&housekeeping_overridden)) {
 		if (housekeeping.flags & BIT(type)) {
-			cpu = sched_numa_find_closest(housekeeping.cpumasks[type], smp_processor_id());
+			cpu = sched_numa_find_closest(housekeeping_cpumask(type), smp_processor_id());
 			if (cpu < nr_cpu_ids)
 				return cpu;
 
-			cpu = cpumask_any_and_distribute(housekeeping.cpumasks[type], cpu_online_mask);
+			cpu = cpumask_any_and_distribute(housekeeping_cpumask(type), cpu_online_mask);
 			if (likely(cpu < nr_cpu_ids))
 				return cpu;
 			/*
@@ -59,28 +70,18 @@ int housekeeping_any_cpu(enum hk_type type)
 }
 EXPORT_SYMBOL_GPL(housekeeping_any_cpu);
 
-const struct cpumask *housekeeping_cpumask(enum hk_type type)
-{
-	if (static_branch_unlikely(&housekeeping_overridden))
-		if (housekeeping.flags & BIT(type))
-			return housekeeping.cpumasks[type];
-	return cpu_possible_mask;
-}
-EXPORT_SYMBOL_GPL(housekeeping_cpumask);
-
 void housekeeping_affine(struct task_struct *t, enum hk_type type)
 {
 	if (static_branch_unlikely(&housekeeping_overridden))
 		if (housekeeping.flags & BIT(type))
-			set_cpus_allowed_ptr(t, housekeeping.cpumasks[type]);
+			set_cpus_allowed_ptr(t, housekeeping_cpumask(type));
 }
 EXPORT_SYMBOL_GPL(housekeeping_affine);
 
 bool housekeeping_test_cpu(int cpu, enum hk_type type)
 {
-	if (static_branch_unlikely(&housekeeping_overridden))
-		if (housekeeping.flags & BIT(type))
-			return cpumask_test_cpu(cpu, housekeeping.cpumasks[type]);
+	if (static_branch_unlikely(&housekeeping_overridden) && housekeeping.flags & BIT(type))
+		return cpumask_test_cpu(cpu, housekeeping_cpumask(type));
 	return true;
 }
 EXPORT_SYMBOL_GPL(housekeeping_test_cpu);
@@ -96,20 +97,33 @@ void __init housekeeping_init(void)
 
 	if (housekeeping.flags & HK_FLAG_KERNEL_NOISE)
 		sched_tick_offload_init();
-
+	/*
+	 * Realloc with a proper allocator so that any cpumask update
+	 * can indifferently free the old version with kfree().
+	 */
 	for_each_set_bit(type, &housekeeping.flags, HK_TYPE_MAX) {
+		struct cpumask *omask, *nmask = kmalloc(cpumask_size(), GFP_KERNEL);
+
+		if (WARN_ON_ONCE(!nmask))
+			return;
+
+		omask = rcu_dereference(housekeeping.cpumasks[type]);
+
 		/* We need at least one CPU to handle housekeeping work */
-		WARN_ON_ONCE(cpumask_empty(housekeeping.cpumasks[type]));
+		WARN_ON_ONCE(cpumask_empty(omask));
+		cpumask_copy(nmask, omask);
+		RCU_INIT_POINTER(housekeeping.cpumasks[type], nmask);
+		memblock_free(omask, cpumask_size());
 	}
 }
 
 static void __init housekeeping_setup_type(enum hk_type type,
 					   cpumask_var_t housekeeping_staging)
 {
+	struct cpumask *mask = memblock_alloc_or_panic(cpumask_size(), SMP_CACHE_BYTES);
 
-	alloc_bootmem_cpumask_var(&housekeeping.cpumasks[type]);
-	cpumask_copy(housekeeping.cpumasks[type],
-		     housekeeping_staging);
+	cpumask_copy(mask, housekeeping_staging);
+	RCU_INIT_POINTER(housekeeping.cpumasks[type], mask);
 }
 
 static int __init housekeeping_setup(char *str, unsigned long flags)
@@ -162,7 +176,7 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
 
 		for_each_set_bit(type, &iter_flags, HK_TYPE_MAX) {
 			if (!cpumask_equal(housekeeping_staging,
-					   housekeeping.cpumasks[type])) {
+					   housekeeping_cpumask(type))) {
 				pr_warn("Housekeeping: nohz_full= must match isolcpus=\n");
 				goto free_housekeeping_staging;
 			}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d30cca6870f5..475bdab3b8db 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -42,6 +42,7 @@
 #include <linux/ktime_api.h>
 #include <linux/lockdep_api.h>
 #include <linux/lockdep.h>
+#include <linux/memblock.h>
 #include <linux/minmax.h>
 #include <linux/mm.h>
 #include <linux/module.h>
-- 
2.51.1

On Thu, Jan 01, 2026 at 11:13:38PM +0100, Frederic Weisbecker wrote:
> HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
> A synchronization mechanism is then needed to synchronize the updates
> with the housekeeping cpumask readers.
> 
> Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
> cpumask will be modified, the update side will wait for an RCU grace
> period and propagate the change to interested subsystem when deemed
> necessary.
> 
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>  kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
>  kernel/sched/sched.h     |  1 +
>  2 files changed, 37 insertions(+), 22 deletions(-)
> 
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 11a623fa6320..83be49ec2b06 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
>  EXPORT_SYMBOL_GPL(housekeeping_overridden);
>  
>  struct housekeeping {
> -	cpumask_var_t cpumasks[HK_TYPE_MAX];
> +	struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
>  	unsigned long flags;
>  };
>  
> @@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
>  }
>  EXPORT_SYMBOL_GPL(housekeeping_enabled);
>  
> +const struct cpumask *housekeeping_cpumask(enum hk_type type)
> +{
> +	if (static_branch_unlikely(&housekeeping_overridden)) {
> +		if (housekeeping.flags & BIT(type)) {
> +			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
> +		}
> +	}
> +	return cpu_possible_mask;
> +}
> +EXPORT_SYMBOL_GPL(housekeeping_cpumask);
> +

Hi Frederic,

I think this patch should also update the access to housekeeping.cpumasks
in housekeeping_setup(), on line 200, to use housekeeping_cpumask().

As is, sparse flags __rcu a annotation miss match there.

  kernel/sched/isolation.c:200:80: warning: incorrect type in argument 3 (different address spaces)
  kernel/sched/isolation.c:200:80:    expected struct cpumask const *srcp3
  kernel/sched/isolation.c:200:80:    got struct cpumask [noderef] __rcu *

...

On 1/7/26 6:56 AM, Simon Horman wrote:
> On Thu, Jan 01, 2026 at 11:13:38PM +0100, Frederic Weisbecker wrote:
>> HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
>> A synchronization mechanism is then needed to synchronize the updates
>> with the housekeeping cpumask readers.
>>
>> Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
>> cpumask will be modified, the update side will wait for an RCU grace
>> period and propagate the change to interested subsystem when deemed
>> necessary.
>>
>> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
>> ---
>>   kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
>>   kernel/sched/sched.h     |  1 +
>>   2 files changed, 37 insertions(+), 22 deletions(-)
>>
>> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
>> index 11a623fa6320..83be49ec2b06 100644
>> --- a/kernel/sched/isolation.c
>> +++ b/kernel/sched/isolation.c
>> @@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
>>   EXPORT_SYMBOL_GPL(housekeeping_overridden);
>>   
>>   struct housekeeping {
>> -	cpumask_var_t cpumasks[HK_TYPE_MAX];
>> +	struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
>>   	unsigned long flags;
>>   };
>>   
>> @@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
>>   }
>>   EXPORT_SYMBOL_GPL(housekeeping_enabled);
>>   
>> +const struct cpumask *housekeeping_cpumask(enum hk_type type)
>> +{
>> +	if (static_branch_unlikely(&housekeeping_overridden)) {
>> +		if (housekeeping.flags & BIT(type)) {
>> +			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
>> +		}
>> +	}
>> +	return cpu_possible_mask;
>> +}
>> +EXPORT_SYMBOL_GPL(housekeeping_cpumask);
>> +
> Hi Frederic,
>
> I think this patch should also update the access to housekeeping.cpumasks
> in housekeeping_setup(), on line 200, to use housekeeping_cpumask().
>
> As is, sparse flags __rcu a annotation miss match there.
>
>    kernel/sched/isolation.c:200:80: warning: incorrect type in argument 3 (different address spaces)
>    kernel/sched/isolation.c:200:80:    expected struct cpumask const *srcp3
>    kernel/sched/isolation.c:200:80:    got struct cpumask [noderef] __rcu *
>
> ...
>
The direct housekeeping.cpumasks[type] reference is in the newly merged 
check after Federic's initial patch series.

                 iter_flags = housekeeping.flags & (HK_FLAG_KERNEL_NOISE 
| HK_FLAG_DOMAIN);
                 type = find_first_bit(&iter_flags, HK_TYPE_MAX);
                 /*
                  * Pass the check if none of these flags were 
previously set or
                  * are not in the current selection.
                  */
                 iter_flags = flags & (HK_FLAG_KERNEL_NOISE | 
HK_FLAG_DOMAIN);
                 first_cpu = (type == HK_TYPE_MAX || !iter_flags) ? 0 :
cpumask_first_and_and(cpu_present_mask,
                                     housekeeping_staging, 
housekeeping.cpumasks[type]);

Maybe that is why it is missed.

Cheers,
Longman

Le Sun, Jan 11, 2026 at 09:45:36PM -0500, Waiman Long a écrit :
> On 1/7/26 6:56 AM, Simon Horman wrote:
> > On Thu, Jan 01, 2026 at 11:13:38PM +0100, Frederic Weisbecker wrote:
> > > HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
> > > A synchronization mechanism is then needed to synchronize the updates
> > > with the housekeeping cpumask readers.
> > > 
> > > Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
> > > cpumask will be modified, the update side will wait for an RCU grace
> > > period and propagate the change to interested subsystem when deemed
> > > necessary.
> > > 
> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > > ---
> > >   kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
> > >   kernel/sched/sched.h     |  1 +
> > >   2 files changed, 37 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> > > index 11a623fa6320..83be49ec2b06 100644
> > > --- a/kernel/sched/isolation.c
> > > +++ b/kernel/sched/isolation.c
> > > @@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
> > >   EXPORT_SYMBOL_GPL(housekeeping_overridden);
> > >   struct housekeeping {
> > > -	cpumask_var_t cpumasks[HK_TYPE_MAX];
> > > +	struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
> > >   	unsigned long flags;
> > >   };
> > > @@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
> > >   }
> > >   EXPORT_SYMBOL_GPL(housekeeping_enabled);
> > > +const struct cpumask *housekeeping_cpumask(enum hk_type type)
> > > +{
> > > +	if (static_branch_unlikely(&housekeeping_overridden)) {
> > > +		if (housekeeping.flags & BIT(type)) {
> > > +			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
> > > +		}
> > > +	}
> > > +	return cpu_possible_mask;
> > > +}
> > > +EXPORT_SYMBOL_GPL(housekeeping_cpumask);
> > > +
> > Hi Frederic,
> > 
> > I think this patch should also update the access to housekeeping.cpumasks
> > in housekeeping_setup(), on line 200, to use housekeeping_cpumask().
> > 
> > As is, sparse flags __rcu a annotation miss match there.
> > 
> >    kernel/sched/isolation.c:200:80: warning: incorrect type in argument 3 (different address spaces)
> >    kernel/sched/isolation.c:200:80:    expected struct cpumask const *srcp3
> >    kernel/sched/isolation.c:200:80:    got struct cpumask [noderef] __rcu *
> > 
> > ...
> > 
> The direct housekeeping.cpumasks[type] reference is in the newly merged
> check after Federic's initial patch series.
> 
>                 iter_flags = housekeeping.flags & (HK_FLAG_KERNEL_NOISE |
> HK_FLAG_DOMAIN);
>                 type = find_first_bit(&iter_flags, HK_TYPE_MAX);
>                 /*
>                  * Pass the check if none of these flags were previously set
> or
>                  * are not in the current selection.
>                  */
>                 iter_flags = flags & (HK_FLAG_KERNEL_NOISE |
> HK_FLAG_DOMAIN);
>                 first_cpu = (type == HK_TYPE_MAX || !iter_flags) ? 0 :
> cpumask_first_and_and(cpu_present_mask,
>                                     housekeeping_staging,
> housekeeping.cpumasks[type]);
> 
> Maybe that is why it is missed.

Good catch guys! Fixing this.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs