Fix typos

core/src/main/scala/org/apache/spark/SparkConf.scala

@@ -621,7 +621,7 @@ private[spark] object SparkConf extends Logging {
   /**
    * Return whether the given config should be passed to an executor on start-up.
    *
-   * Certain akka and authentication configs are required of the executor when it connects to
+   * Certain akka and authentication configs are required from the executor when it connects to
    * the scheduler, while the rest of the spark configs can be inherited from the driver later.
    */
   def isExecutorStartupConf(name: String): Boolean = {

core/src/main/scala/org/apache/spark/metrics/MetricsSystem.scala

@@ -197,7 +197,7 @@ private[spark] class MetricsSystem private (
           }
         } catch {
           case e: Exception => {
-            logError("Sink class " + classPath + " cannot be instantialized")
+            logError("Sink class " + classPath + " cannot be instantiated")
             throw e
           }
         }

core/src/main/scala/org/apache/spark/scheduler/TaskScheduler.scala

@@ -22,7 +22,8 @@ import org.apache.spark.executor.TaskMetrics
 import org.apache.spark.storage.BlockManagerId
 
 /**
- * Low-level task scheduler interface, currently implemented exclusively by TaskSchedulerImpl.
+ * Low-level task scheduler interface, currently implemented exclusively by
+ * [[org.apache.spark.scheduler.TaskSchedulerImpl]].
  * This interface allows plugging in different task schedulers. Each TaskScheduler schedules tasks
  * for a single SparkContext. These schedulers get sets of tasks submitted to them from the
  * DAGScheduler for each stage, and are responsible for sending the tasks to the cluster, running

core/src/main/scala/org/apache/spark/util/ThreadUtils.scala

@@ -80,7 +80,7 @@ private[spark] object ThreadUtils {
   }
 
   /**
-   * Wrapper over newSingleThreadScheduledExecutor.
+   * Wrapper over ScheduledThreadPoolExecutor.
    */
   def newDaemonSingleThreadScheduledExecutor(threadName: String): ScheduledExecutorService = {
     val threadFactory = new ThreadFactoryBuilder().setDaemon(true).setNameFormat(threadName).build()