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Message-ID: <c6dfcbc9-c7e1-4221-b79c-b4c745e5b167@huaweicloud.com>
Date: Thu, 18 Dec 2025 09:39:43 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <llong@...hat.com>, tj@...nel.org, hannes@...xchg.org,
mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
lujialin4@...wei.com
Subject: Re: [PATCH -next 6/6] cpuset: remove v1-specific code from
generate_sched_domains
On 2025/12/18 3:05, Waiman Long wrote:
> On 12/17/25 3:49 AM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@...wei.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@...wei.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.
>> }
>> csa = kmalloc_array(nr_cpusets(), sizeof(cp), GFP_KERNEL);
>> if (!csa)
>> goto done;
>> - csn = 0;
>> + /* Find how many partitions and cache them to csa[] */
>> rcu_read_lock();
>> - if (root_load_balance)
>> - csa[csn++] = &top_cpuset;
>> cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
>
> The cpuset_for_each_descendant_pre() macro will visit the root (top_cpuset) first and so it should
> be OK to remove the above 2 lines of code.
>
> Cheers,
> Longman
>
--
Best regards,
Ridong
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