Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting after every update

[Waiman Long]

On 3/10/25 3:18 PM, Waiman Long wrote:
> On 3/10/25 2:54 PM, Dietmar Eggemann wrote:
> > On 10/03/2025 10:37, Juri Lelli wrote:
> > > Rebuilding of root domains accounting information (total_bw) is
> > > currently broken on some cases, e.g. suspend/resume on aarch64. Problem
> > Nit: Couldn't spot any arch dependency here. I guess it was just tested
> > on Arm64 platforms so far.
> >
> > [...]
> >
> > > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > > index 44093339761c..363ad268a25b 100644
> > > --- a/kernel/sched/topology.c
> > > +++ b/kernel/sched/topology.c
> > > @@ -2791,6 +2791,7 @@ void partition_sched_domains_locked(int 
> > > ndoms_new, cpumask_var_t doms_new[],
> > >       ndoms_cur = ndoms_new;
> > >         update_sched_domain_debugfs();
> > > +    dl_rebuild_rd_accounting();
> > Won't dl_rebuild_rd_accounting()'s lockdep_assert_held(&cpuset_mutex)
> > barf when called via cpuhp's:
> >
> > sched_cpu_deactivate()
> >
> >    cpuset_cpu_inactive()
> >
> >      partition_sched_domains()
> >
> >        partition_sched_domains_locked()
> >
> >          dl_rebuild_rd_accounting()
> >
> > ?
> >
> > [...]
>
> Right. If cpuhp_tasks_frozen is true, partition_sched_domains() will 
> be called without holding cpuset mutex.
>
> Well, I think we will need an additional wrapper in cpuset.c that 
> acquires the cpuset_mutex first before calling 
> partition_sched_domains() and use the new wrapper in these cases.

Actually, partition_sched_domains() is called with the special arguments 
(1, NULL, NULL) to reset the domain to a single one. So perhaps 
something like the following will be enough to avoid this problem.

BTW, we can merge partition_sched_domains_locked() into 
partition_sched_domains() as there is no other caller.

Cheers,
Longman

------------------------------------------------------------------------------------------------

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 95bde793651c..39b9ffa6a39a 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2692,6 +2692,7 @@ static void partition_sched_domains_locked(int 
ndoms_new, cpumask_var_t doms_new
                                    struct sched_domain_attr *dattr_new)
 {
        bool __maybe_unused has_eas = false;
+       bool reset_domain = false;
        int i, j, n;
        int new_topology;

@@ -2706,6 +2707,7 @@ static void partition_sched_domains_locked(int 
ndoms_new, cpumask_var_t doms_new
        if (!doms_new) {
                WARN_ON_ONCE(dattr_new);
                n = 0;
+               reset_domain = true;
                doms_new = alloc_sched_domains(1);
                if (doms_new) {
                        n = 1;
@@ -2778,7 +2780,8 @@ static void partition_sched_domains_locked(int 
ndoms_new, cpumask_var_t doms_new
        ndoms_cur = ndoms_new;

        update_sched_domain_debugfs();
-       dl_rebuild_rd_accounting();
+       if (!reset_domain)
+               dl_rebuild_rd_accounting();
 }

 /*