Re: [PATCH v4 2/9] sched/topology: Extract "imb_numa_nr" calculation into a separate helper

[K Prateek Nayak <kprateek.nayak@amd.com>]

On 3/12/2026 7:07 PM, kernel test robot wrote:
> sparse warnings: (new ones prefixed by >>)
>    kernel/sched/build_utility.c: note: in included file:
>    kernel/sched/debug.c:730:17: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct sched_domain *[assigned] sd @@     got struct sched_domain [noderef] __rcu *parent @@

So what is out official stance on sparse in the sched bits? Because I
can make this go away with:

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 963007d83216..7bf1f830067f 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2591,7 +2591,7 @@ static bool topology_span_sane(const struct cpumask *cpu_map)
  */
 static void adjust_numa_imbalance(struct sched_domain *sd_llc)
 {
-	struct sched_domain *parent;
+	struct sched_domain __rcu *parent;
 	unsigned int imb_span = 1;
 	unsigned int imb = 0;
 	unsigned int nr_llcs;
---

But I can make a ton more go away by doing:

diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 51c29581f15e..7d1efd981caf 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -72,8 +72,8 @@ struct sched_domain_shared {
 
 struct sched_domain {
 	/* These fields must be setup */
-	struct sched_domain __rcu *parent;	/* top domain must be null terminated */
-	struct sched_domain __rcu *child;	/* bottom domain must be null terminated */
+	struct sched_domain *parent;	/* top domain must be null terminated */
+	struct sched_domain *child;	/* bottom domain must be null terminated */
 	struct sched_group *groups;	/* the balancing groups of the domain */
 	unsigned long min_interval;	/* Minimum balance interval ms */
 	unsigned long max_interval;	/* Maximum balance interval ms */
---

"__rcu" evaluates to "noderef, address_space(__rcu)" but we do end up
dereferencing a bunch of these directly (like sd->parent->parent) but
noderef suggests that is illegal?

One place this probably helps is to spot cases where a pointer *needs*
to be accessed via rcu_dereference*() but it isn't - that is indeed nice
to have but ...

Then it also complains about using rcu_dereference*() on pointers that
isn't __rcu annotated but perhaps that is solvable (although some of it
isn't very pretty like "cpumask ** __rcu *sched_domains_numa_masks").
-- 
Thanks and Regards,
Prateek