SERVER-28181 Fix the deadlock in OplogFetcher's constructor.

(cherry picked from commit 7361e94af31142ec018ccad70b0398e3a472eba5)

1 files changed, 7 insertions, 7 deletions

diff --git a/src/mongo/db/repl/bgsync.cpp b/src/mongo/db/repl/bgsync.cpp
index d50d66b6af1..8683fffe24c 100644
--- a/src/mongo/db/repl/bgsync.cpp
+++ b/src/mongo/db/repl/bgsync.cpp
@@ -367,20 +367,18 @@ void BackgroundSync::_produce(OperationContext* opCtx) {
     auto rbidCopyForFetcher = syncSourceResp.rbid;  // OplogFetcher's callback modifies this.
     OplogFetcher* oplogFetcher;
     try {
-        auto executor = _replicationCoordinatorExternalState->getTaskExecutor();
-        auto config = _replCoord->getConfig();
         auto onOplogFetcherShutdownCallbackFn =
             [&fetcherReturnStatus](const Status& status, const OpTimeWithHash& lastFetched) {
                 fetcherReturnStatus = status;
             };
-
-        stdx::lock_guard<stdx::mutex> lock(_mutex);
-        _oplogFetcher = stdx::make_unique<OplogFetcher>(
-            executor,
+        // The construction of OplogFetcher has to be outside bgsync mutex, because it calls
+        // replication coordinator.
+        auto oplogFetcherPtr = stdx::make_unique<OplogFetcher>(
+            _replicationCoordinatorExternalState->getTaskExecutor(),
             OpTimeWithHash(lastHashFetched, lastOpTimeFetched),
             source,
             NamespaceString(rsOplogName),
-            config,
+            _replCoord->getConfig(),
             _replicationCoordinatorExternalState->getOplogFetcherMaxFetcherRestarts(),
             &dataReplicatorExternalState,
             stdx::bind(&BackgroundSync::_enqueueDocuments,
@@ -390,6 +388,8 @@ void BackgroundSync::_produce(OperationContext* opCtx) {
                        stdx::placeholders::_3,
                        &rbidCopyForFetcher),
             onOplogFetcherShutdownCallbackFn);
+        stdx::lock_guard<stdx::mutex> lock(_mutex);
+        _oplogFetcher = std::move(oplogFetcherPtr);
         oplogFetcher = _oplogFetcher.get();
     } catch (const mongo::DBException& ex) {
         fassertFailedWithStatus(34440, exceptionToStatus());