SERVER-34758 Fix to prevent deadlock between initial sync and replSetGetStatus cmd when called along with initialSync:1.

(cherry picked from commit 3c6d6969752ad4322594dab171ca7dd26b854bc8)

1 files changed, 11 insertions, 3 deletions

diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index ad1a9fd93ba..10b60b7a205 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -2077,9 +2077,17 @@ Status ReplicationCoordinatorImpl::processReplSetGetStatus(
 
     BSONObj initialSyncProgress;
     if (responseStyle == ReplSetGetStatusResponseStyle::kInitialSync) {
-        LockGuard lk(_mutex);
-        if (_initialSyncer) {
-            initialSyncProgress = _initialSyncer->getInitialSyncProgress();
+        std::shared_ptr<InitialSyncer> initialSyncerCopy;
+        {
+            LockGuard lk(_mutex);
+            initialSyncerCopy = _initialSyncer;
+        }
+
+        // getInitialSyncProgress must be called outside the ReplicationCoordinatorImpl::_mutex
+        // lock. Else it might deadlock with InitialSyncer::_multiApplierCallback where it first
+        // acquires InitialSyncer::_mutex and then ReplicationCoordinatorImpl::_mutex.
+        if (initialSyncerCopy) {
+            initialSyncProgress = initialSyncerCopy->getInitialSyncProgress();
         }
     }