Currently, nocb_cb_wait() unconditionally acquires the leaf rcu_node
->lock to advance callbacks when done invoking the previous batch.
It does this while holding ->nocb_lock, which means that contention on
the leaf rcu_node ->lock visits itself on the ->nocb_lock. This commit
therefore makes this lock acquisition conditional, forgoing callback
advancement when the leaf rcu_node ->lock is not immediately available.
(In this case, the no-CBs grace-period kthread will eventually do any
needed callback advancement.)
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
kernel/rcu/tree_plugin.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index a1a2fc9df6d8..7fbf2c4411a1 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1803,9 +1803,10 @@ static void nocb_cb_wait(struct rcu_data *rdp)
local_bh_enable();
lockdep_assert_irqs_enabled();
rcu_nocb_lock_irqsave(rdp, flags);
- raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ if (raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
+ needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ }
if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
rcu_nocb_unlock_irqrestore(rdp, flags);
if (needwake_gp)
--
2.17.1
