Commit-ID: 95335c0355834c16cc11f041a981ee6782dba2e9
Gitweb: http://git.kernel.org/tip/95335c0355834c16cc11f041a981ee6782dba2e9
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 26 Jun 2017 10:49:50 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 25 Jul 2017 13:04:46 -0700
rcu: Check for NOCB CPUs and empty lists earlier in CB migration
The current CPU-hotplug RCU-callback-migration code checks
for the source (newly offlined) CPU being a NOCBs CPU down in
rcu_send_cbs_to_orphanage(). This commit simplifies callback migration a
bit by moving this check up to rcu_migrate_callbacks(). This commit also
adds a check for the source CPU having no callbacks, which eases analysis
of the rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() functions.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f5acf34..aeea697 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3862,10 +3862,6 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
{
lockdep_assert_held(&rsp->orphan_lock);
- /* No-CBs CPUs do not have orphanable callbacks. */
- if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))
- return;
-
/*
* Orphan the callbacks. First adjust the counts. This is safe
* because _rcu_barrier() excludes CPU-hotplug operations, so it
@@ -3935,6 +3931,9 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
+ if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
+ return; /* No callbacks to migrate. */
+
raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
rcu_adopt_orphan_cbs(rsp, flags);
--
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