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Mon, 07 Sep 2026 00:59:04 -0700 (PDT) From: Kunwu Chan X-Google-Original-From: Kunwu Chan To: paulmck@kernel.org, jiangshanlai@gmail.com, josh@joshtriplett.org Cc: rostedt@goodmis.org, mathieu.desnoyers@efficios.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, Kunwu Chan Subject: [PATCH 06/13] srcutree: Make init_srcu_struct_atomic() prevent transition to big Date: Mon, 7 Sep 2026 15:58:22 +0800 Message-ID: <20260907075829.2073224-7-kunwu.chan@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260907075829.2073224-1-kunwu.chan@linux.dev> References: <20260907075829.2073224-1-kunwu.chan@linux.dev> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kunwu Chan 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 --- 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