On 1/11/26 9:35 PM, Chen Ridong wrote:
On 2026/1/12 10:29, Chen Ridong wrote:
On 2026/1/10 9:32, Waiman Long wrote:
As stated in commit 1c09b195d37f ("cpuset: fix a regression in validating
config change"), it is not allowed to clear masks of a cpuset if
there're tasks in it. This is specific to v1 since empty "cpuset.cpus"
or "cpuset.mems" will cause the v2 cpuset to inherit the effective CPUs
or memory nodes from its parent. So it is OK to have empty cpus or mems
even if there are tasks in the cpuset.
Move this empty cpus/mems check in validate_change() to
cpuset1_validate_change() to allow more flexibility in setting
cpus or mems in v2. cpuset_is_populated() needs to be moved into
cpuset-internal.h as it is needed by the empty cpus/mems checking code.
Also add a test case to test_cpuset_prs.sh to verify that.
Reported-by: Chen Ridong <[email protected]>
Closes:
https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Waiman Long <[email protected]>
---
kernel/cgroup/cpuset-internal.h | 9 ++++++++
kernel/cgroup/cpuset-v1.c | 14 +++++++++++
kernel/cgroup/cpuset.c | 23 -------------------
.../selftests/cgroup/test_cpuset_prs.sh | 3 +++
4 files changed, 26 insertions(+), 23 deletions(-)
diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index e8e2683cb067..fd7d19842ded 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -260,6 +260,15 @@ static inline int nr_cpusets(void)
return static_key_count(&cpusets_enabled_key.key) + 1;
}
+static inline bool cpuset_is_populated(struct cpuset *cs)
+{
+ lockdep_assert_cpuset_lock_held();
+
+ /* Cpusets in the process of attaching should be considered as
populated */
+ return cgroup_is_populated(cs->css.cgroup) ||
+ cs->attach_in_progress;
+}
+
/**
* cpuset_for_each_child - traverse online children of a cpuset
* @child_cs: loop cursor pointing to the current child
diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
index 04124c38a774..7a23b9e8778f 100644
--- a/kernel/cgroup/cpuset-v1.c
+++ b/kernel/cgroup/cpuset-v1.c
@@ -368,6 +368,20 @@ int cpuset1_validate_change(struct cpuset *cur, struct
cpuset *trial)
if (par && !is_cpuset_subset(trial, par))
goto out;
+ /*
+ * Cpusets with tasks - existing or newly being attached - can't
+ * be changed to have empty cpus_allowed or mems_allowed.
+ */
+ ret = -ENOSPC;
+ if (cpuset_is_populated(cur)) {
+ if (!cpumask_empty(cur->cpus_allowed) &&
+ cpumask_empty(trial->cpus_allowed))
+ goto out;
+ if (!nodes_empty(cur->mems_allowed) &&
+ nodes_empty(trial->mems_allowed))
+ goto out;
+ }
+
ret = 0;
out:
return ret;
The current implementation is sufficient.
However, I suggest we fully separate the validation logic for v1 and v2. While
this may introduce
some code duplication (likely minimal), it would allow us to modify the
validate_change logic for v2
in the future without needing to consider v1 compatibility. Given that v1 is
unlikely to see further
changes, this separation would be a practical long-term decision.
@@ -368,6 +368,48 @@ int cpuset1_validate_change(struct cpuset *cur, struct
cpuset *trial)
if (par && !is_cpuset_subset(trial, par))
goto out;
+ /*
+ * Cpusets with tasks - existing or newly being attached - can't
+ * be changed to have empty cpus_allowed or mems_allowed.
+ */
+ ret = -ENOSPC;
+ if (cpuset_is_populated(cur)) {
+ if (!cpumask_empty(cur->cpus_allowed) &&
+ cpumask_empty(trial->cpus_allowed))
+ goto out;
+ if (!nodes_empty(cur->mems_allowed) &&
+ nodes_empty(trial->mems_allowed))
+ goto out;
+ }
+
+ /*
+ * We can't shrink if we won't have enough room for SCHED_DEADLINE
+ * tasks. This check is not done when scheduling is disabled as the
+ * users should know what they are doing.
+ *
+ * For v1, effective_cpus == cpus_allowed & user_xcpus() returns
+ * cpus_allowed.
+ *
+ */
+ ret = -EBUSY;
+ if (is_cpu_exclusive(cur) && is_sched_load_balance(cur) &&
+ !cpuset_cpumask_can_shrink(cur->effective_cpus, user_xcpus(trial)))
+ goto out;
+
+ /*
+ * If either I or some sibling (!= me) is exclusive, we can't
+ * overlap. exclusive_cpus cannot overlap with each other if set.
+ */
+ ret = -EINVAL;
+ cpuset_for_each_child(c, css, par) {
+ if (c == cur)
+ continue;
+ if (cpuset1_cpus_excl_conflict(trial, c))
+ goto out;
+ if (mems_excl_conflict(trial, c))
+ goto out;
+ }
+
ret = 0;
out:
return ret;
A major redundancy is in the cpuset_cpumask_can_shrink check. By placing
cpuset1_cpus_excl_conflict
within the v1 path, we could simplify the overall cpus_excl_conflict function
as well.
This is additional cleanup work. It can be done as a follow-on patch
later on.
Cheers,
Longman
