rcu_tree: Avoid touching rnp->completed when a new GP is started

In rcu_gp_init(), rnp->completed equals to rsp->completed in THEORY,
we don't need to touch it normally.  If something goes wrong,
it will complain and fixup rnp->completed and avoid oops.
This commit thus avoids the normal needless store to rnp->completed.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 48d640c..077d0b7 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1757,8 +1757,8 @@ static int rcu_gp_init(struct rcu_state *rsp)
                rcu_preempt_check_blocked_tasks(rnp);
                rnp->qsmask = rnp->qsmaskinit;
                ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
-               WARN_ON_ONCE(rnp->completed != rsp->completed);
-               ACCESS_ONCE(rnp->completed) = rsp->completed;
+               if (WARN_ON_ONCE(rnp->completed != rsp->completed))
+                       ACCESS_ONCE(rnp->completed) = rsp->completed;
                if (rnp == rdp->mynode)
                        (void)__note_gp_changes(rsp, rnp, rdp);
                rcu_preempt_boost_start_gp(rnp);