rcu: Short-circuit synchronize_sched_expedited() if only one CPU

If there is only one CPU, then invoking synchronize_sched_expedited()
is by definition a grace period.  This commit checks for this condition
and does a short-circuit return in that case.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 81aa1cdc6bc99b1f164aeb2dd1178764b914913b..bd2605c144ccf208b298c7c2694d881528a72add 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3822,6 +3822,10 @@ void synchronize_sched_expedited(void)
        struct rcu_node *rnp;
        struct rcu_state *rsp = &rcu_sched_state;
 
+       /* If only one CPU, this is automatically a grace period. */
+       if (rcu_blocking_is_gp())
+               return;
+
        /* Take a snapshot of the sequence number.  */
        s = rcu_exp_gp_seq_snap(rsp);