linux-kernel - [RFC PATCH 6/8] rcuscale: Allow rcu_scale_ops::get_gp

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Message-ID: <20250414060055.341516-7-boqun.feng@gmail.com>
Date: Sun, 13 Apr 2025 23:00:53 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Breno Leitao <leitao@...ian.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>
Cc: aeh@...a.com,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	edumazet@...gle.com,
	jhs@...atatu.com,
	kernel-team@...a.com,
	Erik Lundgren <elundgren@...a.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Uladzislau Rezki <urezki@...il.com>,
	rcu@...r.kernel.org,
	Boqun Feng <boqun.feng@...il.com>
Subject: [RFC PATCH 6/8] rcuscale: Allow rcu_scale_ops::get_gp_seq to be NULL

For synchronization mechanisms similar to RCU, there could be no "grace
period" concept (e.g. hazard pointers), therefore allow
rcu_scale_ops::get_gp_seq to be a NULL pointer for these cases, and
simply treat started and finished grace period as 0.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/rcuscale.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 0f3059b1b80d..d9bff4b1928b 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -568,8 +568,10 @@ rcu_scale_writer(void *arg)
 		if (gp_exp) {
 			b_rcu_gp_test_started =
 				cur_ops->exp_completed() / 2;
-		} else {
+		} else if (cur_ops->get_gp_seq) {
 			b_rcu_gp_test_started = cur_ops->get_gp_seq();
+		} else {
+			b_rcu_gp_test_started = 0;
 		}
 	}
 
@@ -625,9 +627,11 @@ rcu_scale_writer(void *arg)
 				if (gp_exp) {
 					b_rcu_gp_test_finished =
 						cur_ops->exp_completed() / 2;
-				} else {
+				} else if (cur_ops->get_gp_seq) {
 					b_rcu_gp_test_finished =
 						cur_ops->get_gp_seq();
+				} else {
+					b_rcu_gp_test_finished = 0;
 				}
 				if (shutdown) {
 					smp_mb(); /* Assign before wake. */
-- 
2.47.1