linux-kernel - Re: [PATCH 14/33] cpuset: Update HK_TYPE

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Message-ID: <17aadc7e-7dd6-4335-a748-e66f0239df85@redhat.com>
Date: Thu, 25 Dec 2025 21:24:41 -0500
From: Waiman Long <llong@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Michal Koutný <mkoutny@...e.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Catalin Marinas <catalin.marinas@....com>,
 Chen Ridong <chenridong@...wei.com>, Danilo Krummrich <dakr@...nel.org>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Gabriele Monaco <gmonaco@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ingo Molnar <mingo@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>,
 Lai Jiangshan <jiangshanlai@...il.com>,
 Marco Crivellari <marco.crivellari@...e.com>, Michal Hocko
 <mhocko@...e.com>, Muchun Song <muchun.song@...ux.dev>,
 Paolo Abeni <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Phil Auld <pauld@...hat.com>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Simon Horman <horms@...nel.org>,
 Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
 cgroups@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-block@...r.kernel.org, linux-mm@...ck.org, linux-pci@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH 14/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset

On 12/24/25 8:45 AM, 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@...nel.org>
> ---
>   include/linux/sched/isolation.h |  7 +++
>   kernel/cgroup/cpuset.c          |  3 ++
>   kernel/sched/isolation.c        | 76 ++++++++++++++++++++++++++++++---
>   kernel/sched/sched.h            |  1 +
>   4 files changed, 81 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index 109a2149e21a..6842a1ba4d13 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -9,6 +9,11 @@
>   enum hk_type {
>   	/* Revert of boot-time isolcpus= argument */
>   	HK_TYPE_DOMAIN_BOOT,
> +	/*
> +	 * Same as HK_TYPE_DOMAIN_BOOT but also includes the
> +	 * revert of cpuset isolated partitions. As such it
> +	 * is always a subset of HK_TYPE_DOMAIN_BOOT.
> +	 */
>   	HK_TYPE_DOMAIN,
>   	/* Revert of boot-time isolcpus=managed_irq argument */
>   	HK_TYPE_MANAGED_IRQ,
> @@ -35,6 +40,7 @@ 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 *isol_mask, enum hk_type type);
>   extern void __init housekeeping_init(void);
>   
>   #else
> @@ -62,6 +68,7 @@ static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
>   	return true;
>   }
>   
> +static inline int housekeeping_update(struct cpumask *isol_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 5e2e3514c22e..e13e32491ebf 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1490,6 +1490,9 @@ static void update_isolation_cpumasks(void)
>   	ret = tmigr_isolated_exclude_cpumask(isolated_cpus);
>   	WARN_ON_ONCE(ret < 0);
>   
> +	ret = housekeeping_update(isolated_cpus, HK_TYPE_DOMAIN);
> +	WARN_ON_ONCE(ret < 0);
> +
>   	isolated_cpus_updating = false;
>   }
>   
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 83be49ec2b06..a124f1119f2e 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) {

To be more correct, we should use IS_ENABLED(CONFIG_PROVE_LOCKING) as 
this is the real kconfig that enables most of the lockdep checking. 
PROVE_LOCKING selects LOCKDEP but not vice versa. So for some weird 
configs that set LOCKDEP but not PROVE_LOCKING, it can cause compilation 
problem.

Other than that, the rest looks good to me.

Cheers,
Longman