[PATCH 17/19] srcutree: Make init_srcu_struct_atomic() prevent transition to big

[Paul E. McKenney]

From: Kunwu Chan <kunwu.chan@xxxxxxxxx>

The is_atomic parameter of init_srcu_struct_fields() exists so that
atomic SRCU never transitions to big, but neither
init_srcu_struct_atomic() nor its lockdep counterpart
__init_srcu_struct_atomic() sets it.

On systems where srcutree.convert_to_big selects SRCU_SIZING_INIT,
this needlessly allocates a full srcu_node combining tree for any
dynamically initialized atomic srcu_struct, despite atomic SRCU
having neither callbacks nor srcu_barrier() operations.

Pass true from both atomic entry points, adding an is_atomic parameter
to __init_srcu_struct_common().

Signed-off-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/srcutree.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 82e61421142e..4e9a0b8ea344 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -305,26 +305,27 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static, bool
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 static int
-__init_srcu_struct_common(struct srcu_struct *ssp, const char *name, struct lock_class_key *key)
+__init_srcu_struct_common(struct srcu_struct *ssp, const char *name,
+			  struct lock_class_key *key, bool is_atomic)
 {
 	/* Don't re-initialize a lock while it is held. */
 	debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
 	lockdep_init_map(&ssp->dep_map, name, key, 0);
-	return init_srcu_struct_fields(ssp, false, false);
+	return init_srcu_struct_fields(ssp, false, is_atomic);
 }
 
 int init_srcu_struct_lockdep(struct srcu_struct *ssp, const char *name,
 			     struct lock_class_key *key)
 {
 	ssp->srcu_reader_flavor = 0;
-	return __init_srcu_struct_common(ssp, name, key);
+	return __init_srcu_struct_common(ssp, name, key, false);
 }
 EXPORT_SYMBOL_GPL(init_srcu_struct_lockdep);
 
 int __init_srcu_struct_fast(struct srcu_struct *ssp, const char *name, struct lock_class_key *key)
 {
 	ssp->srcu_reader_flavor = SRCU_READ_FLAVOR_FAST;
-	return __init_srcu_struct_common(ssp, name, key);
+	return __init_srcu_struct_common(ssp, name, key, false);
 }
 EXPORT_SYMBOL_GPL(__init_srcu_struct_fast);
 
@@ -332,14 +333,14 @@ int __init_srcu_struct_fast_updown(struct srcu_struct *ssp, const char *name,
 				   struct lock_class_key *key)
 {
 	ssp->srcu_reader_flavor = SRCU_READ_FLAVOR_FAST_UPDOWN;
-	return __init_srcu_struct_common(ssp, name, key);
+	return __init_srcu_struct_common(ssp, name, key, false);
 }
 EXPORT_SYMBOL_GPL(__init_srcu_struct_fast_updown);
 
 int __init_srcu_struct_atomic(struct srcu_struct *ssp, const char *name, struct lock_class_key *key)
 {
 	ssp->srcu_reader_flavor = SRCU_READ_FLAVOR_ATOMIC;
-	return __init_srcu_struct_common(ssp, name, key);
+	return __init_srcu_struct_common(ssp, name, key, true);
 }
 EXPORT_SYMBOL_GPL(__init_srcu_struct_atomic);
 
@@ -414,7 +415,7 @@ EXPORT_SYMBOL_GPL(init_srcu_struct_fast_updown);
 int init_srcu_struct_atomic(struct srcu_struct *ssp)
 {
 	ssp->srcu_reader_flavor = SRCU_READ_FLAVOR_ATOMIC;
-	return init_srcu_struct_fields(ssp, false, false);
+	return init_srcu_struct_fields(ssp, false, true);
 }
 EXPORT_SYMBOL_GPL(init_srcu_struct_atomic);
 
-- 
2.40.1