Re: [PATCH 13/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset

Waiman Long
2025-10-21T04:10:28Z

On 10/13/25 4:31 PM, Frederic Weisbecker wrote:
> Until now, HK_TYPE_DOMAIN used to only include boot defined isolated
> CPUs passed through isolcpus= boot option. Users interested in also
> knowing the runtime defined isolated CPUs through cpuset must use
> different APIs: cpuset_cpu_is_isolated(), cpu_is_isolated(), etc...
>
> There are many drawbacks to that approach:
>
> 1) Most interested subsystems want to know about all isolated CPUs, not
> just those defined on boot time.
>
> 2) cpuset_cpu_is_isolated() / cpu_is_isolated() are not synchronized with
> concurrent cpuset changes.
>
> 3) Further cpuset modifications are not propagated to subsystems
>
> Solve 1) and 2) and centralize all isolated CPUs within the
> HK_TYPE_DOMAIN housekeeping cpumask.
>
> Subsystems can rely on RCU to synchronize against concurrent changes.
>
> The propagation mentioned in 3) will be handled in further patches.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
> include/linux/sched/isolation.h | 2 +
> kernel/cgroup/cpuset.c | 2 +
> kernel/sched/isolation.c | 75 ++++++++++++++++++++++++++++++---
> kernel/sched/sched.h | 1 +
> 4 files changed, 74 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index da22b038942a..94d5c835121b 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -32,6 +32,7 @@ extern const struct cpumask *housekeeping_cpumask(enum hk_type type);
> extern bool housekeeping_enabled(enum hk_type type);
> extern void housekeeping_affine(struct task_struct *t, enum hk_type type);
> extern bool housekeeping_test_cpu(int cpu, enum hk_type type);
> +extern int housekeeping_update(struct cpumask *mask, enum hk_type type);
> extern void __init housekeeping_init(void);
>
> #else
> @@ -59,6 +60,7 @@ static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
> return true;
> }
>
> +static inline int housekeeping_update(struct cpumask *mask, enum hk_type type) { return 0; }
> static inline void housekeeping_init(void) { }
> #endif /* CONFIG_CPU_ISOLATION */
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index aa1ac7bcf2ea..b04a4242f2fa 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1403,6 +1403,8 @@ static void update_unbound_workqueue_cpumask(bool isolcpus_updated)
>
> ret = workqueue_unbound_exclude_cpumask(isolated_cpus);
> WARN_ON_ONCE(ret < 0);
> + ret = housekeeping_update(isolated_cpus, HK_TYPE_DOMAIN);
> + WARN_ON_ONCE(ret < 0);
> }
>
> /**
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index b46c20b5437f..95d69c2102f6 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -29,18 +29,48 @@ static struct housekeeping housekeeping;
>
> bool housekeeping_enabled(enum hk_type type)
> {
> - return !!(housekeeping.flags & BIT(type));
> + return !!(READ_ONCE(housekeeping.flags) & BIT(type));
> }
> EXPORT_SYMBOL_GPL(housekeeping_enabled);
>
> +static bool housekeeping_dereference_check(enum hk_type type)
> +{
> + if (IS_ENABLED(CONFIG_LOCKDEP) && type == HK_TYPE_DOMAIN) {
> + /* Cpuset isn't even writable yet? */
> + if (system_state <= SYSTEM_SCHEDULING)
> + return true;
> +
> + /* CPU hotplug write locked, so cpuset partition can't be overwritten */
> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_write_held())
> + return true;
> +
> + /* Cpuset lock held, partitions not writable */
> + if (IS_ENABLED(CONFIG_CPUSETS) && lockdep_is_cpuset_held())
> + return true;

I have some doubt about this condition as the cpuset_mutex may be held
in the process of making changes to an isolated partition that will
impact HK_TYPE_DOMAIN cpumask.

Cheers,
Longman