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authorPaul E. McKenney <paulmck@kernel.org>2024-10-28 17:22:51 -0700
committerFrederic Weisbecker <frederic@kernel.org>2024-11-03 21:55:35 +0100
commit9650edd9bf1d152f69ccf96b67c4e28577a4cf98 (patch)
tree39ca3e79cc930be1fed7c8ccb5afefb52d8a8009 /kernel/rcu
parentcbe644aa6fe176bdeb7e175bb194ad644d65319f (diff)
downloadlwn-9650edd9bf1d152f69ccf96b67c4e28577a4cf98.tar.gz
lwn-9650edd9bf1d152f69ccf96b67c4e28577a4cf98.zip
rcu: Finer-grained grace-period-end checks in rcu_dump_cpu_stacks()
This commit pushes the grace-period-end checks further down into rcu_dump_cpu_stacks(), and also uses lockless checks coupled with finer-grained locking. The result is that the current leaf rcu_node structure's ->lock is acquired only if a stack backtrace might be needed from the current CPU, and is held across only that CPU's backtrace. As a result, if there are no stalled CPUs associated with a given rcu_node structure, then its ->lock will not be acquired at all. On large systems, it is usually (though not always) the case that a small number of CPUs are stalling the current grace period, which means that the ->lock need be acquired only for a small fraction of the rcu_node structures. [ paulmck: Apply Dan Carpenter feedback. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree_stall.h18
1 files changed, 11 insertions, 7 deletions
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index b530844becf8..925fcdad5dea 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -342,20 +342,24 @@ static void rcu_dump_cpu_stacks(unsigned long gp_seq)
struct rcu_node *rnp;
rcu_for_each_leaf_node(rnp) {
- if (gp_seq != data_race(rcu_state.gp_seq)) {
- pr_err("INFO: Stall ended during stack backtracing.\n");
- return;
- }
printk_deferred_enter();
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- for_each_leaf_node_possible_cpu(rnp, cpu)
+ for_each_leaf_node_possible_cpu(rnp, cpu) {
+ if (gp_seq != data_race(rcu_state.gp_seq)) {
+ printk_deferred_exit();
+ pr_err("INFO: Stall ended during stack backtracing.\n");
+ return;
+ }
+ if (!(data_race(rnp->qsmask) & leaf_node_cpu_bit(rnp, cpu)))
+ continue;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
if (cpu_is_offline(cpu))
pr_err("Offline CPU %d blocking current GP.\n", cpu);
else
dump_cpu_task(cpu);
}
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
printk_deferred_exit();
}
}