[SPARK-14252] Executors do not try to download remote cached blocks

## What changes were proposed in this pull request?

As mentioned in the ticket this was because one get path in the refactored `BlockManager` did not check for remote storage.

## How was this patch tested?

Unit test, also verified manually with reproduction in the ticket.

cc JoshRosen

Author: Eric Liang <ekl@databricks.com>

Closes #12193 from ericl/spark-14252.

core/src/main/scala/org/apache/spark/storage/BlockManager.scala

@@ -643,6 +643,14 @@ private[spark] class BlockManager(
       level: StorageLevel,
       classTag: ClassTag[T],
       makeIterator: () => Iterator[T]): Either[BlockResult, Iterator[T]] = {
+    // Attempt to read the block from local or remote storage. If it's present, then we don't need
+    // to go through the local-get-or-put path.
+    get(blockId) match {
+      case Some(block) =>
+        return Left(block)
+      case _ =>
+        // Need to compute the block.
+    }
     // Initially we hold no locks on this block.
     doPutIterator(blockId, makeIterator, level, classTag, keepReadLock = true) match {
       case None =>

core/src/test/scala/org/apache/spark/storage/BlockManagerSuite.scala

@@ -515,6 +515,19 @@ class BlockManagerSuite extends SparkFunSuite with Matchers with BeforeAndAfterE
     }
   }
 
+  test("SPARK-14252: getOrElseUpdate should still read from remote storage") {
+    store = makeBlockManager(8000, "executor1")
+    store2 = makeBlockManager(8000, "executor2")
+    val list1 = List(new Array[Byte](4000))
+    store2.putIterator(
+      "list1", list1.iterator, StorageLevel.MEMORY_ONLY, tellMaster = true)
+    assert(store.getOrElseUpdate(
+      "list1",
+      StorageLevel.MEMORY_ONLY,
+      ClassTag.Any,
+      () => throw new AssertionError("attempted to compute locally")).isLeft)
+  }
+
   test("in-memory LRU storage") {
     testInMemoryLRUStorage(StorageLevel.MEMORY_ONLY)
   }