On Tue, 8 Sep 2026 16:36:11 -0700 "Paul E. McKenney" <[email protected]> wrote:
> On Mon, Sep 07, 2026 at 03:58:22PM +0800, Kunwu Chan wrote: > > From: Kunwu Chan <[email protected]> > > > > 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 <[email protected]> > > Given that we have this commit, is this patch needed? > > 4e01d5320a2f ("srcutree: Suppress to-big transition for atomic SRCU") > > If so, please tell me what I am missing. Yes, this patch is still needed. The is_atomic mechanism is there, but the atomic initialization paths still pass false. In particular, init_srcu_struct_atomic() passes false directly, while the lockdep path goes through __init_srcu_struct_common(), which also passes false. This patch makes both atomic entry points propagate true. Thanks, KunWu > > Thanx, Paul > > > --- > > 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 2af36db37fa9..01f224a56b41 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); > > > > -- > > 2.43.0 > > >
