cpuset: Make cpuset hotplug synchronous

Convert cpuset_hotplug_workfn() into synchronous call for cpu hotplug
path. For memory hotplug path it still gets queued as a work item.

Since cpuset_hotplug_workfn() can be made synchronous for cpu hotplug
path, it is not required to wait for cpuset hotplug while thawing
processes.

Signed-off-by: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 20 insertions, 21 deletions

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index cab5fd1ee767..227bc25d951d 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2277,15 +2277,8 @@ retry:
         mutex_unlock(&cpuset_mutex);
 }
 
-static bool force_rebuild;
-
-void cpuset_force_rebuild(void)
-{
-        force_rebuild = true;
-}
-
 /**
- * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
+ * cpuset_hotplug - handle CPU/memory hotunplug for a cpuset
  *
  * This function is called after either CPU or memory configuration has
  * changed and updates cpuset accordingly.  The top_cpuset is always
@@ -2300,7 +2293,7 @@ void cpuset_force_rebuild(void)
  * Note that CPU offlining during suspend is ignored.  We don't modify
  * cpusets across suspend/resume cycles at all.
  */
-static void cpuset_hotplug_workfn(struct work_struct *work)
+static void cpuset_hotplug(bool use_cpu_hp_lock)
 {
         static cpumask_t new_cpus;
         static nodemask_t new_mems;
@@ -2358,25 +2351,31 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
         }
 
         /* rebuild sched domains if cpus_allowed has changed */
-        if (cpus_updated || force_rebuild) {
-                force_rebuild = false;
-                rebuild_sched_domains();
+        if (cpus_updated) {
+                if (use_cpu_hp_lock)
+                        rebuild_sched_domains();
+                else {
+                        /* Acquiring cpu_hotplug_lock is not required.
+                         * When cpuset_hotplug() is called in hotplug path,
+                         * cpu_hotplug_lock is held by the hotplug context
+                         * which is waiting for cpuhp_thread_fun to indicate
+                         * completion of callback.
+                         */
+                        mutex_lock(&cpuset_mutex);
+                        rebuild_sched_domains_cpuslocked();
+                        mutex_unlock(&cpuset_mutex);
+                }
         }
 }
 
-void cpuset_update_active_cpus(void)
+static void cpuset_hotplug_workfn(struct work_struct *work)
 {
-        /*
-         * We're inside cpu hotplug critical region which usually nests
-         * inside cgroup synchronization.  Bounce actual hotplug processing
-         * to a work item to avoid reverse locking order.
-         */
-        schedule_work(&cpuset_hotplug_work);
+        cpuset_hotplug(true);
 }
 
-void cpuset_wait_for_hotplug(void)
+void cpuset_update_active_cpus(void)
 {
-        flush_work(&cpuset_hotplug_work);
+        cpuset_hotplug(false);
 }
 
 /*