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

[Paul E. McKenney]

On Sat, Oct 03, 2026 at 06:52:44PM +0100, Bradley Morgan wrote:
> 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.

Take it easy, Bradley.

Many in the Linux kernel community consider it polite to drop a tag
from (or, as in this case, avoid adding a tag to) a patch that changed
significantly.  On the CC issue, you did find the patch the first time
without him CCing you.  ;-)

Kunwu did nothing wrong here.

							Thanx, Paul

> >---
> >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