From: Waiman Long <longman@redhat.com>
To: Guopeng Zhang <guopeng.zhang@linux.dev>,
ridong.chen@linux.dev, cgroups@vger.kernel.org
Cc: tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com,
linux-kernel@vger.kernel.org,
Guopeng Zhang <zhangguopeng@kylinos.cn>
Subject: Re: [PATCH] cgroup/cpuset: Use WRITE_ONCE() for shared prs_err updates
Date: Mon, 10 Aug 2026 11:22:25 -0400 [thread overview]
Message-ID: <ae497c54-cc58-4524-b2a6-e92519ee22bb@redhat.com> (raw)
In-Reply-To: <20260810095559.77345-1-guopeng.zhang@linux.dev>
On 8/10/26 5:55 AM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> cpuset_partition_show() reads cs->prs_err without cpuset_mutex using
> READ_ONCE(). The field is documented as not lock protected, but several
> updates to live cpusets still use plain stores.
>
> Convert the remaining prs_err stores on live cpusets to WRITE_ONCE().
>
> Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2")
> Assisted-by: LLM
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
> kernel/cgroup/cpuset.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 0a0fffb5673c..2f7faa795664 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1587,7 +1587,7 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
> cpumask_copy(cs->effective_xcpus, tmp->new_cpus);
> spin_unlock_irq(&callback_lock);
> cpuset_force_rebuild();
> - cs->prs_err = 0;
> + WRITE_ONCE(cs->prs_err, 0);
>
> /*
> * Propagate changes in top_cpuset's effective_cpus down the hierarchy.
> @@ -1661,7 +1661,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
> WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus));
>
> if (cpumask_empty(excpus)) {
> - cs->prs_err = PERR_CPUSEMPTY;
> + WRITE_ONCE(cs->prs_err, PERR_CPUSEMPTY);
> goto invalidate;
> }
>
> @@ -1676,13 +1676,13 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
> if (adding) {
> WARN_ON_ONCE(cpumask_intersects(tmp->addmask, subpartitions_cpus));
> if (!capable(CAP_SYS_ADMIN))
> - cs->prs_err = PERR_ACCESS;
> + WRITE_ONCE(cs->prs_err, PERR_ACCESS);
> else if (cpumask_intersects(tmp->addmask, subpartitions_cpus) ||
> cpumask_subset(top_cpuset.effective_cpus, tmp->addmask))
> - cs->prs_err = PERR_NOCPUS;
> + WRITE_ONCE(cs->prs_err, PERR_NOCPUS);
> else if ((prs == PRS_ISOLATED) &&
> !isolated_cpus_can_update(tmp->addmask, tmp->delmask))
> - cs->prs_err = PERR_HKEEPING;
> + WRITE_ONCE(cs->prs_err, PERR_HKEEPING);
> if (cs->prs_err)
> goto invalidate;
> }
> @@ -2110,13 +2110,13 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
> * partition root.
> */
> WARN_ON_ONCE(is_remote_partition(child));
> - child->prs_err = 0;
> + WRITE_ONCE(child->prs_err, 0);
> if (!cpumask_subset(child->effective_xcpus,
> cs->effective_xcpus))
> - child->prs_err = PERR_INVCPUS;
> + WRITE_ONCE(child->prs_err, PERR_INVCPUS);
> else if (populated &&
> cpumask_subset(new_ecpus, child->effective_xcpus))
> - child->prs_err = PERR_NOCPUS;
> + WRITE_ONCE(child->prs_err, PERR_NOCPUS);
>
> if (child->prs_err) {
> int old_prs = child->partition_root_state;
> @@ -2420,8 +2420,10 @@ static void partition_cpus_change(struct cpuset *cs, struct cpuset *trialcs,
> return;
>
> prs_err = validate_partition(cs, trialcs);
> - if (prs_err)
> - trialcs->prs_err = cs->prs_err = prs_err;
> + if (prs_err) {
> + WRITE_ONCE(cs->prs_err, prs_err);
> + trialcs->prs_err = prs_err;
> + }
>
> if (is_remote_partition(cs)) {
> if (trialcs->prs_err)
> @@ -3944,7 +3946,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
> if (remote && (cpumask_empty(subpartitions_cpus) ||
> (cpumask_empty(&new_cpus) &&
> partition_is_populated(cs, NULL)))) {
> - cs->prs_err = PERR_HOTPLUG;
> + WRITE_ONCE(cs->prs_err, PERR_HOTPLUG);
> remote_partition_disable(cs, tmp);
> compute_effective_cpumask(&new_cpus, cs, parent);
> remote = false;
LGTM
Reviewed-by: Waiman Long <longman@redhat.com>
next prev parent reply other threads:[~2026-08-10 15:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-10 9:55 [PATCH] cgroup/cpuset: Use WRITE_ONCE() for shared prs_err updates Guopeng Zhang
2026-08-10 15:22 ` Waiman Long [this message]
2026-08-10 19:35 ` Tejun Heo
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