Re: [PATCH v2] rcuscale: add srcua scale type

[Bradley Morgan]

On 3 October 2026 17:17:19 BST, Kunwu Chan <kunwu.chan@xxxxxxxxx> wrote:
>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@xxxxxxxxxx>
>Signed-off-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>

1: why didn't u cc me
2: why did you ommit my tag? I tend to review based on correctness, cuz idk pauls preferences, once I do I'll be a better rcu reviewer.

>---
>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@xxxxxxxxx/
>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
>

--- Thanks!
"I'm not a very positive person" - Linus torvalds