SERVER-54652 Create oplog buffer outside of TenantMigrationRecipientService mutex

1 files changed, 5 insertions, 3 deletions

diff --git a/src/mongo/db/repl/tenant_migration_recipient_service.cpp b/src/mongo/db/repl/tenant_migration_recipient_service.cpp
index e251adc76c8..297ee928c6f 100644
--- a/src/mongo/db/repl/tenant_migration_recipient_service.cpp
+++ b/src/mongo/db/repl/tenant_migration_recipient_service.cpp
@@ -784,11 +784,13 @@ void TenantMigrationRecipientService::Instance::_startOplogFetcher() {
     options.dropCollectionAtStartup = false;
     options.dropCollectionAtShutdown = false;
     options.useTemporaryCollection = false;
-    stdx::unique_lock lk(_mutex);
-    invariant(_stateDoc.getStartFetchingDonorOpTime());
+    // Create the oplog buffer outside the mutex to avoid deadlock on a concurrent stepdown.
     auto oplogBufferNS = getOplogBufferNs(getMigrationUUID());
-    _donorOplogBuffer = std::make_unique<OplogBufferCollection>(
+    auto bufferCollection = std::make_unique<OplogBufferCollection>(
         StorageInterface::get(opCtx.get()), oplogBufferNS, options);
+    stdx::unique_lock lk(_mutex);
+    invariant(_stateDoc.getStartFetchingDonorOpTime());
+    _donorOplogBuffer = std::move(bufferCollection);
 
     {
         // Ensure we are primary when trying to startup and create the oplog buffer collection.