From: Zqiang <qiang1.zhang@xxxxxxxxx>
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@xxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8e880c09ab59..e80e8f128c57 100644
--- 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);
--
2.40.0.rc1.284.g88254d51c5-goog
