Re: [PATCH -next 6/6] cpuset: remove v1-specific code from generate_sched_domains
From: Waiman Long
Date: Wed Dec 17 2025 - 22:14:36 EST
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@xxxxxxxxxx>
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@xxxxxxxxxx>
---
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