[PATCH RFC 4/5] sched/topology: Annonate RCU pointers properly

["Joel Fernandes (Google)" <joel@joelfernandes.org>]

The scheduler's topology code uses rcu_assign_pointer() to initialize
various pointers.

Let us annotate the pointers correctly which also help avoid future
bugs. This suppresses the new sparse errors caused by an annotation
check I added to rcu_assign_pointer().

Also replace rcu_assign_pointer call on rq->sd with WRITE_ONCE. This
should be sufficient for the rq->sd initialization.

This fixes sparse errors:
kernel//sched/topology.c:378:9: sparse: error: incompatible types in
comparison expression (different address spaces)
kernel//sched/topology.c:387:9: sparse: error: incompatible types in
comparison expression (different address spaces)
kernel//sched/topology.c:612:9: sparse: error: incompatible types in
comparison expression (different address spaces)
kernel//sched/topology.c:615:9: sparse: error: incompatible types in
comparison expression (different address spaces)
kernel//sched/topology.c:618:9: sparse: error: incompatible types in
comparison expression (different address spaces)
kernel//sched/topology.c:621:9: sparse: error: incompatible types in
comparison expression (different address spaces)

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/sched/sched.h    | 12 ++++++------
 kernel/sched/topology.c | 12 ++++++------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 2ab545d40381..806703afd4b0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -780,7 +780,7 @@ struct root_domain {
 	 * NULL-terminated list of performance domains intersecting with the
 	 * CPUs of the rd. Protected by RCU.
 	 */
-	struct perf_domain	*pd;
+	struct perf_domain __rcu *pd;
 };
 
 extern struct root_domain def_root_domain;
@@ -1305,13 +1305,13 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
 	return sd;
 }
 
-DECLARE_PER_CPU(struct sched_domain *, sd_llc);
+DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DECLARE_PER_CPU(int, sd_llc_size);
 DECLARE_PER_CPU(int, sd_llc_id);
-DECLARE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
-DECLARE_PER_CPU(struct sched_domain *, sd_numa);
-DECLARE_PER_CPU(struct sched_domain *, sd_asym_packing);
-DECLARE_PER_CPU(struct sched_domain *, sd_asym_cpucapacity);
+DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
+DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
+DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
+DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 extern struct static_key_false sched_asym_cpucapacity;
 
 struct sched_group_capacity {
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 3f35ba1d8fde..2eab2e16ded5 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -586,13 +586,13 @@ static void destroy_sched_domains(struct sched_domain *sd)
  * the cpumask of the domain), this allows us to quickly tell if
  * two CPUs are in the same cache domain, see cpus_share_cache().
  */
-DEFINE_PER_CPU(struct sched_domain *, sd_llc);
+DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
 DEFINE_PER_CPU(int, sd_llc_size);
 DEFINE_PER_CPU(int, sd_llc_id);
-DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
-DEFINE_PER_CPU(struct sched_domain *, sd_numa);
-DEFINE_PER_CPU(struct sched_domain *, sd_asym_packing);
-DEFINE_PER_CPU(struct sched_domain *, sd_asym_cpucapacity);
+DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
+DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa);
+DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
+DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
 DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);
 
 static void update_top_cache_domain(int cpu)
@@ -668,7 +668,7 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 
 	rq_attach_root(rq, rd);
 	tmp = rq->sd;
-	rcu_assign_pointer(rq->sd, sd);
+	WRITE_ONCE(rq->sd, sd);
 	dirty_sched_domain_sysctl(cpu);
 	destroy_sched_domains(tmp);
 
-- 
2.21.0.rc0.258.g878e2cd30e-goog