Re: [PATCH v3 4/4] cpuset: generalize the validate_partition() interface
From: Ridong Chen
Date: Tue Nov 10 2026 - 01:37:29 EST
On 11/9/2026 10:52 PM, Waiman Long wrote:
On 11/7/26 7:01 AM, Ridong Chen wrote:Hi Longman,
From: Chen Ridong <chenridong@xxxxxxxxxx>
Refactor validate_partition() to take the parent partition, the new
partition root state, the new effective exclusive CPUs and the CPUs to
be deleted, instead of a trial cpuset. A NULL parent stands for a
remote partition, whose CPUs come from top_cpuset. This makes the
interface flexible enough to handle both local and remote partition
validation.
The no CPU left for tasks check now uses the given parent instead of
parent_cs(cs), and top_cpuset for a remote partition, as that is where
its CPUs are taken from. The cgroup parent of a remote partition does
not give it any CPU.
The housekeeping conflict check is folded into validate_partition(). It
is skipped when the parent is not a valid partition root, as @cs can't
be a valid local partition in that case.
Use the new interface for local partition enablement in
update_parent_effective_cpumask() and in partition_cpus_change(),
replacing the open-coded checks there. The order of the checks is now
the same for both paths: empty CPUs, housekeeping conflict, then no CPU
left for tasks.
Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 119 ++++++++++++++++++++---------------------
1 file changed, 59 insertions(+), 60 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index fc9de6e16ff5..0ec20412b3ce 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1414,6 +1414,48 @@ static bool prstate_housekeeping_conflict(int new_prs, int parent_prs,
return res;
}
+/**
+ * validate_partition - Validate a cpuset partition configuration
+ * @cs: The cpuset to validate
+ * @parent: Parent partition of @cs, NULL for remote partition
+ * @new_prs: The proposed new partition root state
+ * @new_excpus: The new effective exclusive CPUs mask to validate
+ * @del: exclusive CPUs to be deleted from @cs, can be NULL
+ *
+ * A remote partition gets its CPUs from top_cpuset, so top_cpuset is used
+ * as the parent when @parent is NULL.
+ *
+ * The housekeeping check is skipped if @parent is not a valid partition
+ * root as @cs can't be a valid local partition in that case.
+ *
+ * Return: PRS error code (0 if valid, non-zero error code if invalid)
+ */
+static enum prs_errcode validate_partition(struct cpuset *cs,
+ struct cpuset *parent, int new_prs,
+ struct cpumask *new_excpus,
+ struct cpumask *del)
+{
+ int parent_prs;
+
+ if (new_prs == PRS_MEMBER)
+ return PERR_NONE;
+
+ if (cpumask_empty(new_excpus))
+ return PERR_INVCPUS;
+
+ if (!parent)
+ parent = &top_cpuset;
+ parent_prs = parent->partition_root_state;
+ if (parent_prs > 0 &&
+ prstate_housekeeping_conflict(new_prs, parent_prs, new_excpus, del))
+ return PERR_HKEEPING;
+
+ if (tasks_nocpu_error(parent, cs, new_excpus))
+ return PERR_NOCPUS;
+
+ return PERR_NONE;
+}
+
/*
* cpuset_update_sd_hk_unlock - Rebuild sched domains, update HK & unlock
*
@@ -1934,18 +1976,10 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) {
new_prs = (cmd == partcmd_enable) ? PRS_ROOT : PRS_ISOLATED;
- /*
- * Enabling partition root is not allowed if its
- * effective_xcpus is empty.
- */
- if (cpumask_empty(tmp->delmask))
- return PERR_INVCPUS;
-
- if (prstate_housekeeping_conflict(new_prs, parent_prs, tmp->delmask, NULL))
- return PERR_HKEEPING;
-
- if (nocpu)
- return PERR_NOCPUS;
+ part_error = validate_partition(cs, parent, new_prs,
+ tmp->delmask, NULL);
+ if (part_error)
+ return part_error;
/*
* This function will only be called when all the preliminary
@@ -2424,32 +2458,6 @@ static int parse_cpuset_cpulist(const char *buf, struct cpumask *out_mask)
return 0;
}
-/**
- * validate_partition - Validate a cpuset partition configuration
- * @cs: The cpuset to validate
- * @trialcs: The trial cpuset containing proposed configuration changes
- *
- * If any validation check fails, the appropriate error code is set in the
- * cpuset's prs_err field.
- *
- * Return: PRS error code (0 if valid, non-zero error code if invalid)
- */
-static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *trialcs)
-{
- struct cpuset *parent = parent_cs(cs);
-
- if (cs_is_member(trialcs))
- return PERR_NONE;
-
- if (cpumask_empty(trialcs->effective_xcpus))
- return PERR_INVCPUS;
-
- if (tasks_nocpu_error(parent, cs, trialcs->effective_xcpus))
- return PERR_NOCPUS;
-
- return PERR_NONE;
-}
-
/**
* partition_cpus_change - Handle partition state changes due to CPU mask updates
* @cs: The target cpuset being modified
@@ -2463,33 +2471,24 @@ static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
struct tmpmasks *tmp)
{
enum prs_errcode prs_err;
- int parent_prs = is_remote_partition(cs)
- ? PRS_ROOT : parent_cs(cs)->partition_root_state;
+ struct cpuset *parent = is_remote_partition(cs) ? NULL : parent_cs(cs);
if (cs_is_member(cs))
return;
- prs_err = validate_partition(cs, trialcs);
- if (!prs_err && (parent_prs > 0) &&
- !cpumask_empty(trialcs->effective_xcpus)) {
- int prs = cs->partition_root_state;
-
- /*
- * Check for housekeeping conflict by passing the whole
- * effective_xcpus as well as those CPUs that are to be
- * removed from cs as delmask.
- */
- if (prs > 0)
- cpumask_andnot(tmp->delmask, cs->effective_xcpus,
- trialcs->effective_xcpus);
- else
- cpumask_clear(tmp->delmask);
-
- if (prstate_housekeeping_conflict(prs, parent_prs,
- trialcs->effective_xcpus, tmp->delmask))
- prs_err = PERR_HKEEPING;
- }
+ /*
+ * Check for housekeeping conflict by passing the whole
+ * effective_xcpus as well as those CPUs that are to be
+ * removed from cs as delmask.
+ */
+ if (is_partition_valid(cs))
+ cpumask_andnot(tmp->delmask, cs->effective_xcpus,
+ trialcs->effective_xcpus);
+ else
+ cpumask_clear(tmp->delmask);
+ prs_err = validate_partition(cs, parent, trialcs->partition_root_state,
+ trialcs->effective_xcpus, tmp->delmask);
if (prs_err) {
WRITE_ONCE(cs->prs_err, prs_err);
trialcs->prs_err = prs_err;
Again, this code change looks good to me. Similar to previous patch, it includes both code restructuring and bug fixes.
Thanks for the review. Yes, besides the restructuring, it fixes a false
PERR_NOCPUS error for remote partitions. The no CPU left for tasks check
in partition_cpus_change() is done against the cgroup parent, but the
CPUs of a remote partition come from top_cpuset, not from its parent.
It can be reproduced on a 4-CPU system:
cd /sys/fs/cgroup
echo +cpuset > cgroup.subtree_control
mkdir P
echo 2-3 > P/cpuset.cpus
echo 2-3 > P/cpuset.cpus.exclusive
echo +cpuset > P/cgroup.subtree_control
mkdir P/C
echo 2-3 > P/C/cpuset.cpus
echo 2 > P/C/cpuset.cpus.exclusive
echo root > P/C/cpuset.cpus.partition
sleep 1000 &
echo $! > P/cgroup.procs
echo 2-3 > P/C/cpuset.cpus.exclusive
cat P/C/cpuset.cpus.partition
root invalid (Parent is not a partition root)
The effective_cpus of P is 3, a subset of the new exclusive CPUs 2-3 of
C, and P has a task, so the expansion is rejected. However, P is not a
partition root and does not give any CPU to C, and top_cpuset still has
CPUs 0-1 for the task. Enabling C directly with exclusive CPUs 2-3
succeeds, as remote_partition_enable() checks top_cpuset instead. With
this patch, the expansion succeeds too:
cat P/C/cpuset.cpus.partition
root
The issue has been there since remote partitions were introduced. I
reproduced it on commit 181c8e091aae as well, so I'd like to describe
it in the commit message and add
Fixes: 181c8e091aae ("cgroup/cpuset: Introduce remote partition")
in the next version.
Does that look OK to you? Please let me know if you are referring to something else.
--
Best regards
Ridong