[PATCH v2] rcuscale: add srcua scale type

[Kunwu Chan <kunwu.chan@gmail.com>]

Add support for scaling atomic SRCU grace periods using
srcu_read_lock_atomic()/srcu_read_unlock_atomic() and
synchronize_srcu_atomic().

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
Changes since v1:
- Rename srcu_atomic_ctlp to srcua and reuse srcu_ctlp for
  SRCU operations, as suggested by Paul.
- Reuse the existing SRCU cleanup and completed helpers by
  initializing srcu_ctlp in srcu_atomic_scale_init().
- Add .stats using srcu_scale_stats().
- Use "srcua" to match the existing "srcu" and "srcud" scale
  type names.
- Use synchronize_srcu_atomic() for both normal and expedited
  scale tests.

v1: https://lore.kernel.org/all/20260927100359.3903688-1-kunwu.chan@gmail.com/
Tested with kvm.sh --torture rcuscale scale_type=srcua on x86_64 and
arm64, alongside gp_exp=1 and PROVE_LOCKING=y: no warnings or lockdep
splats.
---
 kernel/rcu/rcuscale.c | 41 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 1097ec15879c..b172882824ac 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -293,6 +293,44 @@ static struct rcu_scale_ops srcud_ops = {
 	.name		= "srcud"
 };
 
+static struct srcu_struct srcua;
+
+static int srcu_scale_atomic_read_lock(void)
+{
+	return srcu_read_lock_atomic(srcu_ctlp);
+}
+
+static void srcu_scale_atomic_read_unlock(int idx)
+{
+	srcu_read_unlock_atomic(srcu_ctlp, idx);
+}
+
+static void srcu_scale_atomic_synchronize(void)
+{
+	synchronize_srcu_atomic(srcu_ctlp);
+}
+
+static void srcu_atomic_scale_init(void)
+{
+	srcu_ctlp = &srcua;
+	init_srcu_struct_atomic(srcu_ctlp);
+}
+
+static struct rcu_scale_ops srcua_ops = {
+	.ptype		= SRCU_FLAVOR,
+	.init		= srcu_atomic_scale_init,
+	.cleanup	= srcu_sync_scale_cleanup,
+	.readlock	= srcu_scale_atomic_read_lock,
+	.readunlock	= srcu_scale_atomic_read_unlock,
+	.get_gp_seq	= srcu_scale_completed,
+	.gp_diff	= rcu_seq_diff,
+	.exp_completed	= srcu_scale_completed,
+	.sync		= srcu_scale_atomic_synchronize,
+	.exp_sync	= srcu_scale_atomic_synchronize,
+	.stats		= srcu_scale_stats,
+	.name		= "srcua"
+};
+
 #ifdef CONFIG_TASKS_RCU
 
 /*
@@ -1110,7 +1148,8 @@ rcu_scale_init(void)
 	long i;
 	long j;
 	static struct rcu_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcud_ops, TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
+		&rcu_ops, &srcu_ops, &srcua_ops, &srcud_ops,
+		TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
 	};
 
 	if (!torture_init_begin(scale_type, verbose))

base-commit: d21906b0aa1e9573cdb5e7acaca44966b9d1dcd2
-- 
2.43.0