Re: [PATCH 14/33] cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset

[Waiman Long]

On 12/25/25 9:24 PM, Waiman Long wrote:
> 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@xxxxxxxxxx>
> > ---
> >   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. 

I think I get confused too. The various lockdep* helpers should be 
defined when CONFIG_LOCKDEP is enabled even if they may not do anything 
useful. So using IS_ENABLED(CONFIG_LOCKDEP) should be fine. Sorry for 
the noise.

Reviewed-by: Waiman Long <longman@xxxxxxxxxx>