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Message-ID: <f9a3fffb-922c-4d4a-81ad-9eeb489cef07@redhat.com>
Date: Wed, 12 Nov 2025 17:54:12 -0500
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, tj@...nel.org,
hannes@...xchg.org, mkoutny@...e.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH RFC v2 12/22] cpuset: introduce
local_partition_invalidate()
On 10/25/25 2:48 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
>
> Build on the partition_disable() infrastructure introduced in the previous
> patch to handle local partition invalidation.
>
> The local_partition_invalidate() function factors out the local partition
> invalidation logic from update_parent_effective_cpumask(), which delegates
> to partition_disable() to complete the invalidation process.
>
> Additionally, correct the transition logic in cpuset_hotplug_update_tasks()
> when determining whether to transition an invalid partition root, the check
> should be based on non-empty user_cpus rather than non-empty
> effective_xcpus. This correction addresses the scenario where
> exclusive_cpus is not set but cpus_allowed is configured - in this case,
> effective_xcpus may be empty even though the partition should be considered
> for re-enablement. The user_cpus-based check ensures proper partition state
> transitions under these conditions.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
> kernel/cgroup/cpuset.c | 66 +++++++++++++++++++++++++++---------------
> 1 file changed, 43 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index f36d17a4d8cd..73a43ab58f72 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1914,6 +1914,40 @@ static void local_partition_disable(struct cpuset *cs, enum prs_errcode part_err
> }
> }
>
> +/**
> + * local_partition_invalidate - Invalidate a local partition
> + * @cs: Target cpuset (local partition root) to invalidate
> + * @tmp: Temporary masks
> + */
> +static void local_partition_invalidate(struct cpuset *cs, struct tmpmasks *tmp)
> +{
> + struct cpumask *xcpus = user_xcpus(cs);
> + struct cpuset *parent = parent_cs(cs);
> + int new_prs = cs->partition_root_state;
> + bool cpumask_updated = false;
> +
> + lockdep_assert_held(&cpuset_mutex);
> + WARN_ON_ONCE(is_remote_partition(cs)); /* For local partition only */
> +
> + if (!is_partition_valid(cs))
> + return;
> +
> + /*
> + * Make the current partition invalid.
> + */
> + if (is_partition_valid(parent))
> + cpumask_updated = cpumask_and(tmp->addmask,
> + xcpus, parent->effective_xcpus);
Invalidation is different from disable. It can be called when parent is
no longer a valid partition root. So the check here is appropriate.
> + if (cs->partition_root_state > 0)
> + new_prs = -cs->partition_root_state;
> +
> + partition_disable(cs, parent, new_prs, cs->prs_err);
> + if (cpumask_updated) {
The cpumask_and() operation above is no longer relevant as it should be
done inside partition_disable(). Instead of cpumask_updated, we can just
do a "is_partition_valid(parent))" check here to decide if the following
two helpers should be called.
Cheers,
Longman
> + cpuset_update_tasks_cpumask(parent, tmp->addmask);
> + update_sibling_cpumasks(parent, cs, tmp);
> + }
> +}
> +
> /**
> * update_parent_effective_cpumask - update effective_cpus mask of parent cpuset
> * @cs: The cpuset that requests change in partition root state
> @@ -1974,22 +2008,6 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
> adding = deleting = false;
> old_prs = new_prs = cs->partition_root_state;
>
> - if (cmd == partcmd_invalidate) {
> - if (is_partition_invalid(cs))
> - return 0;
> -
> - /*
> - * Make the current partition invalid.
> - */
> - if (is_partition_valid(parent))
> - adding = cpumask_and(tmp->addmask,
> - xcpus, parent->effective_xcpus);
> - if (old_prs > 0)
> - new_prs = -old_prs;
> -
> - goto write_error;
> - }
> -
> /*
> * The parent must be a partition root.
> * The new cpumask, if present, or the current cpus_allowed must
> @@ -2553,7 +2571,7 @@ static int cpus_allowed_validate_change(struct cpuset *cs, struct cpuset *trialc
> if (is_partition_valid(cp) &&
> cpumask_intersects(xcpus, cp->effective_xcpus)) {
> rcu_read_unlock();
> - update_parent_effective_cpumask(cp, partcmd_invalidate, NULL, tmp);
> + local_partition_invalidate(cp, tmp);
> rcu_read_lock();
> }
> }
> @@ -2593,8 +2611,7 @@ static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
> trialcs->effective_xcpus, tmp);
> } else {
> if (trialcs->prs_err)
> - update_parent_effective_cpumask(cs, partcmd_invalidate,
> - NULL, tmp);
> + local_partition_invalidate(cs, tmp);
> else
> update_parent_effective_cpumask(cs, partcmd_update,
> trialcs->effective_xcpus, tmp);
> @@ -4040,18 +4057,21 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
> * partitions.
> */
> if (is_local_partition(cs) && (!is_partition_valid(parent) ||
> - tasks_nocpu_error(parent, cs, &new_cpus)))
> + tasks_nocpu_error(parent, cs, &new_cpus))) {
> partcmd = partcmd_invalidate;
> + local_partition_invalidate(cs, tmp);
> + }
> /*
> * On the other hand, an invalid partition root may be transitioned
> - * back to a regular one with a non-empty effective xcpus.
> + * back to a regular one with a non-empty user xcpus.
> */
> else if (is_partition_valid(parent) && is_partition_invalid(cs) &&
> - !cpumask_empty(cs->effective_xcpus))
> + !cpumask_empty(user_xcpus(cs))) {
> partcmd = partcmd_update;
> + update_parent_effective_cpumask(cs, partcmd, NULL, tmp);
> + }
>
> if (partcmd >= 0) {
> - update_parent_effective_cpumask(cs, partcmd, NULL, tmp);
> if ((partcmd == partcmd_invalidate) || is_partition_valid(cs)) {
> compute_partition_effective_cpumask(cs, &new_cpus);
> cpuset_force_rebuild();
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