linux-kernel - Re: [PATCH 13/33] sched/isolation: Convert housekeeping cpumasks to rcu pointers

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Message-ID: <aWVo9em4C3f1TfOQ@pavilion.home>
Date: Mon, 12 Jan 2026 22:34:45 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <llong@...hat.com>
Cc: Simon Horman <horms@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	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>, 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] sched/isolation: Convert housekeeping cpumasks to
 rcu pointers

Le Sun, Jan 11, 2026 at 09:45:36PM -0500, Waiman Long a écrit :
> On 1/7/26 6:56 AM, Simon Horman wrote:
> > On Thu, Jan 01, 2026 at 11:13:38PM +0100, Frederic Weisbecker wrote:
> > > HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
> > > A synchronization mechanism is then needed to synchronize the updates
> > > with the housekeeping cpumask readers.
> > > 
> > > Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
> > > cpumask will be modified, the update side will wait for an RCU grace
> > > period and propagate the change to interested subsystem when deemed
> > > necessary.
> > > 
> > > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > > ---
> > >   kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
> > >   kernel/sched/sched.h     |  1 +
> > >   2 files changed, 37 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> > > index 11a623fa6320..83be49ec2b06 100644
> > > --- a/kernel/sched/isolation.c
> > > +++ b/kernel/sched/isolation.c
> > > @@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
> > >   EXPORT_SYMBOL_GPL(housekeeping_overridden);
> > >   struct housekeeping {
> > > -	cpumask_var_t cpumasks[HK_TYPE_MAX];
> > > +	struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
> > >   	unsigned long flags;
> > >   };
> > > @@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
> > >   }
> > >   EXPORT_SYMBOL_GPL(housekeeping_enabled);
> > > +const struct cpumask *housekeeping_cpumask(enum hk_type type)
> > > +{
> > > +	if (static_branch_unlikely(&housekeeping_overridden)) {
> > > +		if (housekeeping.flags & BIT(type)) {
> > > +			return rcu_dereference_check(housekeeping.cpumasks[type], 1);
> > > +		}
> > > +	}
> > > +	return cpu_possible_mask;
> > > +}
> > > +EXPORT_SYMBOL_GPL(housekeeping_cpumask);
> > > +
> > Hi Frederic,
> > 
> > I think this patch should also update the access to housekeeping.cpumasks
> > in housekeeping_setup(), on line 200, to use housekeeping_cpumask().
> > 
> > As is, sparse flags __rcu a annotation miss match there.
> > 
> >    kernel/sched/isolation.c:200:80: warning: incorrect type in argument 3 (different address spaces)
> >    kernel/sched/isolation.c:200:80:    expected struct cpumask const *srcp3
> >    kernel/sched/isolation.c:200:80:    got struct cpumask [noderef] __rcu *
> > 
> > ...
> > 
> The direct housekeeping.cpumasks[type] reference is in the newly merged
> check after Federic's initial patch series.
> 
>                 iter_flags = housekeeping.flags & (HK_FLAG_KERNEL_NOISE |
> HK_FLAG_DOMAIN);
>                 type = find_first_bit(&iter_flags, HK_TYPE_MAX);
>                 /*
>                  * Pass the check if none of these flags were previously set
> or
>                  * are not in the current selection.
>                  */
>                 iter_flags = flags & (HK_FLAG_KERNEL_NOISE |
> HK_FLAG_DOMAIN);
>                 first_cpu = (type == HK_TYPE_MAX || !iter_flags) ? 0 :
> cpumask_first_and_and(cpu_present_mask,
>                                     housekeeping_staging,
> housekeeping.cpumasks[type]);
> 
> Maybe that is why it is missed.

Good catch guys! Fixing this.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs