* [PATCH] cgroup/cpuset: Use WRITE_ONCE() for shared prs_err updates
@ 2026-08-10 9:55 Guopeng Zhang
2026-08-10 15:22 ` Waiman Long
2026-08-10 19:35 ` Tejun Heo
0 siblings, 2 replies; 3+ messages in thread
From: Guopeng Zhang @ 2026-08-10 9:55 UTC (permalink / raw)
To: longman, ridong.chen, cgroups
Cc: tj, hannes, mkoutny, linux-kernel, Guopeng Zhang
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;
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] cgroup/cpuset: Use WRITE_ONCE() for shared prs_err updates
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
2026-08-10 19:35 ` Tejun Heo
1 sibling, 0 replies; 3+ messages in thread
From: Waiman Long @ 2026-08-10 15:22 UTC (permalink / raw)
To: Guopeng Zhang, ridong.chen, cgroups
Cc: tj, hannes, mkoutny, linux-kernel, Guopeng Zhang
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>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] cgroup/cpuset: Use WRITE_ONCE() for shared prs_err updates
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
@ 2026-08-10 19:35 ` Tejun Heo
1 sibling, 0 replies; 3+ messages in thread
From: Tejun Heo @ 2026-08-10 19:35 UTC (permalink / raw)
To: Guopeng Zhang
Cc: longman, ridong.chen, cgroups, hannes, mkoutny, linux-kernel,
zhangguopeng
On Mon, Aug 10, 2026 at 05:55:59PM +0800, 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().
Applied to cgroup/for-7.3.
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-08-10 19:35 ` Tejun Heo
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