[RFC PATCH 6/8] rcuscale: Allow rcu_scale_ops::get_gp_seq to be NULL

[Boqun Feng]

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.f...@gmail.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