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Message-ID: <6d046d0a-30d4-429e-8ae3-f00b6149c397@huaweicloud.com>
Date: Wed, 22 Oct 2025 09:36:56 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <llong@...hat.com>, 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>, 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 13/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset
On 2025/10/21 12:10, Waiman Long wrote:
> 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@...nel.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
>
+1
ie. 'echo isolate > cpuset.cpus.partition'
--
Best regards,
Ridong
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