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Message-ID: <5a4927e2-ff7f-4f81-b8e3-183f3acb84f4@redhat.com>
Date: Wed, 17 Dec 2025 22:14:26 -0500
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, 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 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@...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.
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.
Cheers,
Longman
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