[SPARK-8606] Prevent exceptions in RDD.getPreferredLocations() from crashing DAGScheduler

If `RDD.getPreferredLocations()` throws an exception it may crash the DAGScheduler and SparkContext. This patch addresses this by adding a try-catch block.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #7023 from JoshRosen/SPARK-8606 and squashes the following commits:

770b169 [Josh Rosen] Fix getPreferredLocations() DAGScheduler crash with try block.
44a9b55 [Josh Rosen] Add test of a buggy getPartitions() method
19aa9f7 [Josh Rosen] Add (failing) regression test for getPreferredLocations() DAGScheduler crash

(cherry picked from commit 0b5abbf)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>

Author: JoshRosen

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

@@ -886,22 +886,29 @@ class DAGScheduler(
         return
     }
 
-    val tasks: Seq[Task[_]] = stage match {
-      case stage: ShuffleMapStage =>
-        partitionsToCompute.map { id =>
-          val locs = getPreferredLocs(stage.rdd, id)
-          val part = stage.rdd.partitions(id)
-          new ShuffleMapTask(stage.id, taskBinary, part, locs)
-        }
+    val tasks: Seq[Task[_]] = try {
+      stage match {
+        case stage: ShuffleMapStage =>
+          partitionsToCompute.map { id =>
+            val locs = getPreferredLocs(stage.rdd, id)
+            val part = stage.rdd.partitions(id)
+            new ShuffleMapTask(stage.id, taskBinary, part, locs)
+          }
 
-      case stage: ResultStage =>
-        val job = stage.resultOfJob.get
-        partitionsToCompute.map { id =>
-          val p: Int = job.partitions(id)
-          val part = stage.rdd.partitions(p)
-          val locs = getPreferredLocs(stage.rdd, p)
-          new ResultTask(stage.id, taskBinary, part, locs, id)
-        }
+        case stage: ResultStage =>
+          val job = stage.resultOfJob.get
+          partitionsToCompute.map { id =>
+            val p: Int = job.partitions(id)
+            val part = stage.rdd.partitions(p)
+            val locs = getPreferredLocs(stage.rdd, p)
+            new ResultTask(stage.id, taskBinary, part, locs, id)
+          }
+      }
+    } catch {
+      case NonFatal(e) =>
+        abortStage(stage, s"Task creation failed: $e\n${e.getStackTraceString}")
+        runningStages -= stage
+        return
     }
 
     if (tasks.size > 0) {

core/src/test/scala/org/apache/spark/scheduler/DAGSchedulerSuite.scala

@@ -757,6 +757,37 @@ class DAGSchedulerSuite
     assert(sc.parallelize(1 to 10, 2).first() === 1)
   }
 
+  test("getPartitions exceptions should not crash DAGScheduler and SparkContext (SPARK-8606)") {
+    val e1 = intercept[DAGSchedulerSuiteDummyException] {
+      val rdd = new MyRDD(sc, 2, Nil) {
+        override def getPartitions: Array[Partition] = {
+          throw new DAGSchedulerSuiteDummyException
+        }
+      }
+      rdd.reduceByKey(_ + _, 1).count()
+    }
+
+    // Make sure we can still run local commands as well as cluster commands.
+    assert(sc.parallelize(1 to 10, 2).count() === 10)
+    assert(sc.parallelize(1 to 10, 2).first() === 1)
+  }
+
+  test("getPreferredLocations errors should not crash DAGScheduler and SparkContext (SPARK-8606)") {
+    val e1 = intercept[SparkException] {
+      val rdd = new MyRDD(sc, 2, Nil) {
+        override def getPreferredLocations(split: Partition): Seq[String] = {
+          throw new DAGSchedulerSuiteDummyException
+        }
+      }
+      rdd.count()
+    }
+    assert(e1.getMessage.contains(classOf[DAGSchedulerSuiteDummyException].getName))
+
+    // Make sure we can still run local commands as well as cluster commands.
+    assert(sc.parallelize(1 to 10, 2).count() === 10)
+    assert(sc.parallelize(1 to 10, 2).first() === 1)
+  }
+
   test("accumulator not calculated for resubmitted result stage") {
     // just for register
     val accum = new Accumulator[Int](0, AccumulatorParam.IntAccumulatorParam)