rcu: Remove never-set needwake assignment from rcu_report_qs_rdp()

The rcu_accelerate_cbs() function is invoked by rcu_report_qs_rdp()
only if there is a grace period in progress that is still blocked
by at least one CPU on this rcu_node structure.  This means that
rcu_accelerate_cbs() should never return the value true, and thus that
this function should never set the needwake variable and in turn never
invoke rcu_gp_kthread_wake().

This commit therefore removes the needwake variable and the invocation
of rcu_gp_kthread_wake() in favor of a WARN_ON_ONCE() on the call to
rcu_accelerate_cbs().  The purpose of this new WARN_ON_ONCE() is to
detect situations where the system's opinion differs from ours.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8e880c09ab59ed0fab53abd7954e60eaaa2c25f2..e80e8f128c57f4acbc5f3ab1d549edbe0a806554 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1955,7 +1955,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
 {
        unsigned long flags;
        unsigned long mask;
-       bool needwake = false;
        bool needacc = false;
        struct rcu_node *rnp;
 
@@ -1987,7 +1986,12 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
                 * NOCB kthreads have their own way to deal with that...
                 */
                if (!rcu_rdp_is_offloaded(rdp)) {
-                       needwake = rcu_accelerate_cbs(rnp, rdp);
+                       /*
+                        * The current GP has not yet ended, so it
+                        * should not be possible for rcu_accelerate_cbs()
+                        * to return true.  So complain, but don't awaken.
+                        */
+                       WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
                } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
                        /*
                         * ...but NOCB kthreads may miss or delay callbacks acceleration
@@ -1999,8 +2003,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
                rcu_disable_urgency_upon_qs(rdp);
                rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
                /* ^^^ Released rnp->lock */
-               if (needwake)
-                       rcu_gp_kthread_wake();
 
                if (needacc) {
                        rcu_nocb_lock_irqsave(rdp, flags);