Re: [PATCH -next 6/6] cpuset: remove v1-specific code from generate_sched_domains

[Chen Ridong <chenridong@huaweicloud.com>]

On 2025/12/18 11:14, Waiman Long wrote:
> On 12/17/25 8:39 PM, Chen Ridong wrote:
>>
>> On 2025/12/18 3:05, Waiman Long wrote:
>>> On 12/17/25 3:49 AM, Chen Ridong wrote:
>>>> From: Chen Ridong <chenridong@huawei.com>
>>>>
>>>> Following the introduction of cpuset1_generate_sched_domains() for v1
>>>> in the previous patch, v1-specific logic can now be removed from the
>>>> generic generate_sched_domains(). This patch cleans up the v1-only
>>>> code and ensures uf_node is only visible when CONFIG_CPUSETS_V1=y.
>>>>
>>>> Signed-off-by: Chen Ridong <chenridong@huawei.com>
>>>> ---
>>>>    kernel/cgroup/cpuset-internal.h |  10 +--
>>>>    kernel/cgroup/cpuset-v1.c       |   2 +-
>>>>    kernel/cgroup/cpuset.c          | 144 +++++---------------------------
>>>>    3 files changed, 27 insertions(+), 129 deletions(-)
>>>>
>>>> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
>>>> index bd767f8cb0ed..ef7b7c5afd4c 100644
>>>> --- a/kernel/cgroup/cpuset-internal.h
>>>> +++ b/kernel/cgroup/cpuset-internal.h
>>>> @@ -175,14 +175,14 @@ struct cpuset {
>>>>        /* Handle for cpuset.cpus.partition */
>>>>        struct cgroup_file partition_file;
>>>>    -    /* Used to merge intersecting subsets for generate_sched_domains */
>>>> -    struct uf_node node;
>>>> -
>>>>    #ifdef CONFIG_CPUSETS_V1
>>>>        struct fmeter fmeter;        /* memory_pressure filter */
>>>>          /* for custom sched domain */
>>>>        int relax_domain_level;
>>>> +
>>>> +    /* Used to merge intersecting subsets for generate_sched_domains */
>>>> +    struct uf_node node;
>>>>    #endif
>>>>    };
>>>>    @@ -315,8 +315,6 @@ void cpuset1_hotplug_update_tasks(struct cpuset *cs,
>>>>    int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial);
>>>>    void cpuset1_init(struct cpuset *cs);
>>>>    void cpuset1_online_css(struct cgroup_subsys_state *css);
>>>> -void update_domain_attr_tree(struct sched_domain_attr *dattr,
>>>> -                    struct cpuset *root_cs);
>>>>    int cpuset1_generate_sched_domains(cpumask_var_t **domains,
>>>>                struct sched_domain_attr **attributes);
>>>>    @@ -331,8 +329,6 @@ static inline int cpuset1_validate_change(struct cpuset *cur,
>>>>                    struct cpuset *trial) { return 0; }
>>>>    static inline void cpuset1_init(struct cpuset *cs) {}
>>>>    static inline void cpuset1_online_css(struct cgroup_subsys_state *css) {}
>>>> -static inline void update_domain_attr_tree(struct sched_domain_attr *dattr,
>>>> -                    struct cpuset *root_cs) {}
>>>>    static inline int cpuset1_generate_sched_domains(cpumask_var_t **domains,
>>>>                struct sched_domain_attr **attributes) { return 0; };
>>>>    diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
>>>> index 5c0bded46a7c..0226350e704f 100644
>>>> --- a/kernel/cgroup/cpuset-v1.c
>>>> +++ b/kernel/cgroup/cpuset-v1.c
>>>> @@ -560,7 +560,7 @@ update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
>>>>            dattr->relax_domain_level = c->relax_domain_level;
>>>>    }
>>>>    -void update_domain_attr_tree(struct sched_domain_attr *dattr,
>>>> +static void update_domain_attr_tree(struct sched_domain_attr *dattr,
>>>>                        struct cpuset *root_cs)
>>>>    {
>>>>        struct cpuset *cp;
>>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>>>> index 6bb0b201c34b..3e3468d928f3 100644
>>>> --- a/kernel/cgroup/cpuset.c
>>>> +++ b/kernel/cgroup/cpuset.c
>>>> @@ -789,18 +789,13 @@ static int generate_sched_domains(cpumask_var_t **domains,
>>>>    {
>>>>        struct cpuset *cp;    /* top-down scan of cpusets */
>>>>        struct cpuset **csa;    /* array of all cpuset ptrs */
>>>> -    int csn;        /* how many cpuset ptrs in csa so far */
>>>>        int i, j;        /* indices for partition finding loops */
>>>>        cpumask_var_t *doms;    /* resulting partition; i.e. sched domains */
>>>>        struct sched_domain_attr *dattr;  /* attributes for custom domains */
>>>>        int ndoms = 0;        /* number of sched domains in result */
>>>> -    int nslot;        /* next empty doms[] struct cpumask slot */
>>>>        struct cgroup_subsys_state *pos_css;
>>>> -    bool root_load_balance = is_sched_load_balance(&top_cpuset);
>>>> -    bool cgrpv2 = cpuset_v2();
>>>> -    int nslot_update;
>>>>    -    if (!cgrpv2)
>>>> +    if (!cpuset_v2())
>>>>            return cpuset1_generate_sched_domains(domains, attributes);
>>>>          doms = NULL;
>>>> @@ -808,70 +803,25 @@ static int generate_sched_domains(cpumask_var_t **domains,
>>>>        csa = NULL;
>>>>          /* Special case for the 99% of systems with one, full, sched domain */
>>>> -    if (root_load_balance && cpumask_empty(subpartitions_cpus)) {
>>>> -single_root_domain:
>>>> +    if (cpumask_empty(subpartitions_cpus)) {
>>>>            ndoms = 1;
>>>> -        doms = alloc_sched_domains(ndoms);
>>>> -        if (!doms)
>>>> -            goto done;
>>>> -
>>>> -        dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
>>>> -        if (dattr) {
>>>> -            *dattr = SD_ATTR_INIT;
>>>> -            update_domain_attr_tree(dattr, &top_cpuset);
>>>> -        }
>>>> -        cpumask_and(doms[0], top_cpuset.effective_cpus,
>>>> -                housekeeping_cpumask(HK_TYPE_DOMAIN));
>>>> -
>>>> -        goto done;
>>>> +        goto generate_doms;
>>> That is not correct. The code under the generate_doms label will need to access csa[0] which is not
>>> allocated yet and may cause panic. You either need to keep the current code or move it after the csa
>>> allocation and assign top_cpuset to csa[0].
>>>
>> Thank you, Longman.
>>
>> Sorry, I should note that I made a small change. I added a !csa check: if csa is not allocated, then
>> ndoms should equal 1, and we only need the top_cpuset (no csa is indeed required). I think it's
>> cleaner to avoid allocating csa when there's no valid partition.
>>
>> ```
>> +    for (i = 0; i < ndoms; i++) {
>> +        /*
>> +         * The top cpuset may contain some boot time isolated
>> +         * CPUs that need to be excluded from the sched domain.
>> +         */
>> +        if (!csa || csa[i] == &top_cpuset)
>> +            cpumask_and(doms[i], top_cpuset.effective_cpus,
>> +                    housekeeping_cpumask(HK_TYPE_DOMAIN));
>> +        else
>> +            cpumask_copy(doms[i], csa[i]->effective_cpus);
>> +        if (dattr)
>> +            dattr[i] = SD_ATTR_INIT;
>>       }
>> ```
>>
>> Tested with single‑domain generation — no panic or warning observed.
> 
> Yes, !csa check here should be good enough to handle the NULL csa case here. Maybe adding a comment
> in the goto line saying that !csa will be correctly handled.
> 

Good idea, will add.

-- 
Best regards,
Ridong