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

[Chen Ridong]

On 2025/10/21 12:10, Waiman Long wrote:
> On 10/13/25 4:31 PM, Frederic Weisbecker wrote:
>> 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 at 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;
> 
> I have some doubt about this condition as the cpuset_mutex may be held in the process of making
> changes to an isolated partition that will impact HK_TYPE_DOMAIN cpumask.
> 
> Cheers,
> Longman
> 

+1

ie. 'echo isolate > cpuset.cpus.partition'

-- 
Best regards,
Ridong