The force_qs_rnp() function checks for ->qsmask being all zero, that is,
all CPUs for the current rcu_node structure having already passed through
quiescent states. But with RCU-preempt, this is not sufficient to report
quiescent states further up the tree, so there are further checks that
can initiate RCU priority boosting and also for races with CPU-hotplug
operations. However, if neither of these further checks apply, the code
proceeds to carry out a useless scan of an all-zero ->qsmask.
This commit therefore adds code to release the current rcu_node
structure's lock and continue on to the next rcu_node structure, thereby
avoiding this useless scan.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
/* rcu_report_unblock_qs_rnp() rlses ->lock */
continue;
}
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ continue;
}
for_each_leaf_node_possible_cpu(rnp, cpu) {
unsigned long bit = leaf_node_cpu_bit(rnp, cpu);