SERVER-53612: Fix StepDown hangs when all nodes are caught up but none is immediately electable

(cherry picked from commit 6308db5c83a3e95f4532c63df8b635b8090036ae)

4 files changed, 30 insertions, 3 deletions

diff --git a/src/mongo/db/repl/heartbeat_response_action.cpp b/src/mongo/db/repl/heartbeat_response_action.cpp
index c21dbd0cf53..6b6bd4797a8 100644
--- a/src/mongo/db/repl/heartbeat_response_action.cpp
+++ b/src/mongo/db/repl/heartbeat_response_action.cpp
@@ -79,5 +79,9 @@ void HeartbeatResponseAction::setAdvancedOpTime(bool advanced) {
     _advancedOpTime = advanced;
 }
 
+void HeartbeatResponseAction::setBecameElectable(bool becameElectable) {
+    _becameElectable = becameElectable;
+}
+
 }  // namespace repl
 }  // namespace mongo
diff --git a/src/mongo/db/repl/heartbeat_response_action.h b/src/mongo/db/repl/heartbeat_response_action.h
index 9f0b3e4da8c..194b4bb0845 100644
--- a/src/mongo/db/repl/heartbeat_response_action.h
+++ b/src/mongo/db/repl/heartbeat_response_action.h
@@ -105,6 +105,12 @@ public:
      */
     void setAdvancedOpTime(bool advanced);
 
+    /*
+     * Sets whether or not the member has transitioned from unelectable to electable since the last
+     * heartbeat response.
+     */
+    void setBecameElectable(bool becameElectable);
+
     /**
      * Gets the action type of this action.
      */
@@ -136,11 +142,20 @@ public:
         return _advancedOpTime;
     }
 
+    /*
+     * Returns true if the heartbeat response results in the member transitioning from unelectable
+     * to electable.
+     */
+    bool getBecameElectable() const {
+        return _becameElectable;
+    }
+
 private:
     Action _action;
     int _primaryIndex;
     Date_t _nextHeartbeatStartDate;
     bool _advancedOpTime = false;
+    bool _becameElectable = false;
 };
 
 }  // namespace repl
diff --git a/src/mongo/db/repl/replication_coordinator_impl_heartbeat.cpp b/src/mongo/db/repl/replication_coordinator_impl_heartbeat.cpp
index c993d696a0d..0b32eacc507 100644
--- a/src/mongo/db/repl/replication_coordinator_impl_heartbeat.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl_heartbeat.cpp
@@ -237,9 +237,13 @@ void ReplicationCoordinatorImpl::_handleHeartbeatResponse(
 
     if (action.getAction() == HeartbeatResponseAction::NoAction && hbStatusResponse.isOK() &&
         hbStatusResponse.getValue().hasState() &&
-        hbStatusResponse.getValue().getState() != MemberState::RS_PRIMARY &&
-        action.getAdvancedOpTime()) {
-        _updateLastCommittedOpTimeAndWallTime(lk);
+        hbStatusResponse.getValue().getState() != MemberState::RS_PRIMARY) {
+        if (action.getAdvancedOpTime()) {
+            _updateLastCommittedOpTimeAndWallTime(lk);
+        } else if (action.getBecameElectable() && _topCoord->isSteppingDown()) {
+            // Try to wake up the stepDown waiter when a new node becomes electable.
+            _wakeReadyWaiters(lk);
+        }
     }
 
     // Abort catchup if we have caught up to the latest known optime after heartbeat refreshing.
diff --git a/src/mongo/db/repl/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index 1df593d8330..727270bee7d 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -854,6 +854,7 @@ HeartbeatResponseAction TopologyCoordinator::processHeartbeatResponse(
     MemberData& hbData = _memberData.at(memberIndex);
     const MemberConfig member = _rsConfig.getMemberAt(memberIndex);
     bool advancedOpTime = false;
+    bool becameElectable = false;
     if (!hbResponse.isOK()) {
         if (isUnauthorized) {
             hbData.setAuthIssue(now);
@@ -871,7 +872,9 @@ HeartbeatResponseAction TopologyCoordinator::processHeartbeatResponse(
         ReplSetHeartbeatResponse hbr = std::move(hbResponse.getValue());
         LOG(3) << "setUpValues: heartbeat response good for member _id:" << member.getId();
         pingsInConfig++;
+        auto wasUnelectable = hbData.isUnelectable();
         advancedOpTime = hbData.setUpValues(now, std::move(hbr));
+        becameElectable = wasUnelectable && !hbData.isUnelectable();
     }
 
     HeartbeatResponseAction nextAction;
@@ -879,6 +882,7 @@ HeartbeatResponseAction TopologyCoordinator::processHeartbeatResponse(
 
     nextAction.setNextHeartbeatStartDate(nextHeartbeatStartDate);
     nextAction.setAdvancedOpTime(advancedOpTime);
+    nextAction.setBecameElectable(becameElectable);
     return nextAction;
 }