[PATCH RFC v1 1/4] rcu/nocb: Consolidate rcu_nocb_cpu_offload/deoffload functions

[Joel Fernandes]

The rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() functions are
nearly duplicates.

Therefore, extract the common logic into rcu_nocb_cpu_toggle_offload()
which takes an 'offload' boolean, and make both exported functions
simple wrappers.

This eliminates a bunch of duplicate code at the call sites, namely
mutex locking, CPU hotplug locking and CPU online checks.

Signed-off-by: Joel Fernandes <joelagn...@nvidia.com>
---
 kernel/rcu/tree_nocb.h | 89 ++++++++++++++++++++++--------------------
 1 file changed, 46 insertions(+), 43 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index b3337c7231cc..5b041134d6bb 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1081,30 +1081,6 @@ static int rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
        return 0;
 }
 
-int rcu_nocb_cpu_deoffload(int cpu)
-{
-       struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
-       int ret = 0;
-
-       cpus_read_lock();
-       mutex_lock(&rcu_state.nocb_mutex);
-       if (rcu_rdp_is_offloaded(rdp)) {
-               if (!cpu_online(cpu)) {
-                       ret = rcu_nocb_rdp_deoffload(rdp);
-                       if (!ret)
-                               cpumask_clear_cpu(cpu, rcu_nocb_mask);
-               } else {
-                       pr_info("NOCB: Cannot CB-deoffload online CPU %d\n", 
rdp->cpu);
-                       ret = -EINVAL;
-               }
-       }
-       mutex_unlock(&rcu_state.nocb_mutex);
-       cpus_read_unlock();
-
-       return ret;
-}
-EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
-
 static bool rcu_nocb_rdp_offload_wait_cond(struct rcu_data *rdp)
 {
        unsigned long flags;
@@ -1149,27 +1125,54 @@ static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
        return 0;
 }
 
+/* Common helper for CPU offload/deoffload operations. */
+static int rcu_nocb_cpu_toggle_offload(int cpu, bool offload)
+{
+       struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+       bool currently_offloaded;
+       int ret = 0;
+
+       cpus_read_lock();
+       mutex_lock(&rcu_state.nocb_mutex);
+
+       currently_offloaded = rcu_rdp_is_offloaded(rdp);
+
+       /* Already in desired state, nothing to do. */
+       if (currently_offloaded == offload)
+               goto out_unlock;
+
+       if (cpu_online(cpu)) {
+               pr_info("NOCB: Cannot CB-%soffload online CPU %d\n",
+                       offload ? "" : "de", rdp->cpu);
+               ret = -EINVAL;
+               goto out_unlock;
+       }
+
+       if (offload) {
+               ret = rcu_nocb_rdp_offload(rdp);
+               if (!ret)
+                       cpumask_set_cpu(cpu, rcu_nocb_mask);
+       } else {
+               ret = rcu_nocb_rdp_deoffload(rdp);
+               if (!ret)
+                       cpumask_clear_cpu(cpu, rcu_nocb_mask);
+       }
+
+out_unlock:
+       mutex_unlock(&rcu_state.nocb_mutex);
+       cpus_read_unlock();
+       return ret;
+}
+
+int rcu_nocb_cpu_deoffload(int cpu)
+{
+       return rcu_nocb_cpu_toggle_offload(cpu, false /* de-offload */);
+}
+EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
+
 int rcu_nocb_cpu_offload(int cpu)
 {
-       struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
-       int ret = 0;
-
-       cpus_read_lock();
-       mutex_lock(&rcu_state.nocb_mutex);
-       if (!rcu_rdp_is_offloaded(rdp)) {
-               if (!cpu_online(cpu)) {
-                       ret = rcu_nocb_rdp_offload(rdp);
-                       if (!ret)
-                               cpumask_set_cpu(cpu, rcu_nocb_mask);
-               } else {
-                       pr_info("NOCB: Cannot CB-offload online CPU %d\n", 
rdp->cpu);
-                       ret = -EINVAL;
-               }
-       }
-       mutex_unlock(&rcu_state.nocb_mutex);
-       cpus_read_unlock();
-
-       return ret;
+       return rcu_nocb_cpu_toggle_offload(cpu, true /* offload */);
 }
 EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
 
-- 
2.34.1