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rcu: Prevent useless FQS scan after all CPUs have checked in
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>
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@ -2672,6 +2672,8 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp))
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/* rcu_report_unblock_qs_rnp() rlses ->lock */
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continue;
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}
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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continue;
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}
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for_each_leaf_node_possible_cpu(rnp, cpu) {
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unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
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