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srcutree: Make init_srcu_struct_atomic() prevent transition to big

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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@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Kunwu Chan 2026-09-07 15:58:22 +08:00 committed by Paul E. McKenney
parent cc7287f9ee
commit cbd520f619
1 changed files with 8 additions and 7 deletions
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15
kernel/rcu/srcutree.c
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@ -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);