Re: [PATCH 2/5] sched/topology: Wrappers for sched_domains_mutex

[Juri Lelli <juri.lelli@xxxxxxxxxx>]

On 05/03/25 10:52, Juri Lelli wrote:
> On 04/03/25 11:01, Waiman Long wrote:
> > On 3/4/25 10:05 AM, Waiman Long wrote:
> > > > --- a/kernel/sched/topology.c
> > > > +++ b/kernel/sched/topology.c
> > > > @@ -6,6 +6,19 @@
> > > >   #include <linux/bsearch.h>
> > > >     DEFINE_MUTEX(sched_domains_mutex);
> > > > +#ifdef CONFIG_SMP
> > > > +void sched_domains_mutex_lock(void)
> > > > +{
> > > > +    mutex_lock(&sched_domains_mutex);
> > > > +}
> > > > +void sched_domains_mutex_unlock(void)
> > > > +{
> > > > +    mutex_unlock(&sched_domains_mutex);
> > > > +}
> > > > +#else
> > > > +void sched_domains_mutex_lock(void) { }
> > > > +void sched_domains_mutex_unlock(void) { }
> > > > +#endif
> > > >     /* Protected by sched_domains_mutex: */
> > > >   static cpumask_var_t sched_domains_tmpmask;
> > > > @@ -2791,7 +2804,7 @@ void partition_sched_domains_locked(int
> > > > ndoms_new, cpumask_var_t doms_new[],
> > > >   void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
> > > >                    struct sched_domain_attr *dattr_new)
> > > >   {
> > > > -    mutex_lock(&sched_domains_mutex);
> > > > +    sched_domains_mutex_lock();
> > > >       partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
> > > > -    mutex_unlock(&sched_domains_mutex);
> > > > +    sched_domains_mutex_unlock();
> > > >   }
> > > 
> > > There are two "lockdep_assert_held(&sched_domains_mutex);" statements in
> > > topology.c file and one in cpuset.c. That can be problematic in the
> > > non-SMP case. Maybe another wrapper to do the assert?
> > 
> > Ignore that as both topology.c and cpuset.c will only be compiled if
> > CONFIG_SMP is defined. IOW, you don't need the the "#ifdef CONFIG_SMP"
> > above.
> 
> Indeed!

Ah, actually I believe next patch (3/5) introduce usage for the !SMP
case in sched_rt_handler()

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4b8e33c615b1..8cebe71d2bb1 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2910,6 +2910,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
        int ret;

        mutex_lock(&mutex);
+       sched_domains_mutex_lock();
        old_period = sysctl_sched_rt_period;
        old_runtime = sysctl_sched_rt_runtime;

@@ -2936,6 +2937,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
                sysctl_sched_rt_period = old_period;
                sysctl_sched_rt_runtime = old_runtime;
        }
+       sched_domains_mutex_unlock();
        mutex_unlock(&mutex);

        return ret;

So, I will need to add the ifdef back I guess (I removed it on v2). Do
you agree?

Thanks,
Juri