rcu: Initialize and destroy rcu_synchronize only when necessary

The __wait_rcu_gp() function unconditionally initializes and cleans up
each element of rs_array[], whether used or not.  This is slightly
wasteful and rather confusing, so this commit skips both initialization
and cleanup for duplicate callback functions.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 84843ad..f5a82e1 100644 (file)
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -390,13 +390,14 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
                        might_sleep();
                        continue;
                }
-               init_rcu_head_on_stack(&rs_array[i].head);
-               init_completion(&rs_array[i].completion);
                for (j = 0; j < i; j++)
                        if (crcu_array[j] == crcu_array[i])
                                break;
-               if (j == i)
+               if (j == i) {
+                       init_rcu_head_on_stack(&rs_array[i].head);
+                       init_completion(&rs_array[i].completion);
                        (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
+               }
        }
 
        /* Wait for all callbacks to be invoked. */
@@ -407,9 +408,10 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
                for (j = 0; j < i; j++)
                        if (crcu_array[j] == crcu_array[i])
                                break;
-               if (j == i)
+               if (j == i) {
                        wait_for_completion(&rs_array[i].completion);
-               destroy_rcu_head_on_stack(&rs_array[i].head);
+                       destroy_rcu_head_on_stack(&rs_array[i].head);
+               }
        }
 }
 EXPORT_SYMBOL_GPL(__wait_rcu_gp);