Deflake ExternalSSTFileTest.PickedLevelBug (#8307)

Summary:
The test want to make sure these's no compaction during `AddFile`
(between `DBImpl::AddFile:MutexLock` and `DBImpl::AddFile:MutexUnlock`)
but the mutex could be unlocked by `EnterUnbatched()`.
Move the lock start point after bumping the ingest file number.

Also fix the dead lock when ASSERT fails.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8307

Reviewed By: ajkr

Differential Revision: D28479849

Pulled By: jay-zhuang

fbshipit-source-id: b3c50f66aa5d5f59c5c27f815bfea189c4cd06cb

db/external_sst_file_test.cc

@@ -1291,8 +1291,11 @@ TEST_F(ExternalSSTFileTest, PickedLevelBug) {
   // We have 2 overlapping files in L0
   EXPECT_EQ(FilesPerLevel(), "2");
 
+  ASSERT_OK(dbfull()->TEST_WaitForCompact());
+
   ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->LoadDependency(
-      {{"DBImpl::AddFile:MutexLock", "ExternalSSTFileTest::PickedLevelBug:0"},
+      {{"DBImpl::IngestExternalFile:AfterIncIngestFileCounter",
+        "ExternalSSTFileTest::PickedLevelBug:0"},
        {"ExternalSSTFileTest::PickedLevelBug:1", "DBImpl::AddFile:MutexUnlock"},
        {"ExternalSSTFileTest::PickedLevelBug:2",
         "DBImpl::RunManualCompaction:0"},
@@ -1333,10 +1336,14 @@ TEST_F(ExternalSSTFileTest, PickedLevelBug) {
     // wait for 2 seconds to give a chance for compactions to run during
     // this period, and then make sure that no compactions where able to run
     env_->SleepForMicroseconds(1000000 * 2);
-    ASSERT_FALSE(bg_compact_started.load());
+    bool bg_compact_started_tmp = bg_compact_started.load();
 
     // Hold AddFile from finishing writing the MANIFEST
     TEST_SYNC_POINT("ExternalSSTFileTest::PickedLevelBug:1");
+
+    // check the status at the end, so even if the ASSERT fails the threads
+    // could be joined and return.
+    ASSERT_FALSE(bg_compact_started_tmp);
   }
 
   ASSERT_OK(bg_addfile_status);