Re: [PATCH v2 4/4] cpuset: generalize the validate_partition() interface

[Ridong Chen]

On 11/7/2026 11:59 AM, Waiman Long wrote:
> On 11/6/26 5:55 AM, Ridong Chen wrote:
> > 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 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 | 112 +++++++++++++++++++----------------------
> >   1 file changed, 52 insertions(+), 60 deletions(-)
> >
> > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> > index a5ab9396eb61..1b0ac4e76ec7 100644
> > --- a/kernel/cgroup/cpuset.c
> > +++ b/kernel/cgroup/cpuset.c
> > @@ -1434,6 +1434,41 @@ 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
> > + *
> > + * 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 = parent ? parent->partition_root_state : PRS_ROOT;
> > +
> > +    if (new_prs == PRS_MEMBER)
> > +        return PERR_NONE;
> > +
> > +    if (cpumask_empty(new_excpus))
> > +        return PERR_INVCPUS;
> > +
> > +    if ((parent_prs > 0) &&
> > +        prstate_housekeeping_conflict(new_prs, parent_prs, new_excpus, del))
> > +        return PERR_HKEEPING;
> > +
> > +    if (tasks_nocpu_error(parent_cs(cs), cs, new_excpus))
> > +        return PERR_NOCPUS;
>
> For remote partition, the parent should be top_cpuset. I think we should set 
> parent to top_cpuset if NULL and pass it directly to tasks_nocpu_error().

Good catch, thanks. parent_cs(cs) is wrong for a remote partition, since
its CPUs come from top_cpuset rather than its cgroup parent. I'll set
parent to &top_cpuset when it's NULL and pass it to tasks_nocpu_error():
	
	  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;

> Other than that, the rests look good to me.

Thanks for the review. Will fix it in v3.

--
Best regards
Ridong