Fix data race in connection

src/server/redis_connection.cc

@@ -77,7 +77,8 @@ void Connection::Close() {
 void Connection::Detach() { owner_->DetachConnection(this); }
 
 void Connection::OnRead(struct bufferevent *bev) {
-  DLOG(INFO) << "[connection] on read: " << bufferevent_getfd(bev);
+  is_running_ = true;
+  MakeScopeExit([this] { is_running_ = false; });
 
   SetLastInteraction();
   auto s = req_.Tokenize(Input());
@@ -178,6 +179,13 @@ void Connection::DisableFlag(Flag flag) { flags_ &= (~flag); }
 
 bool Connection::IsFlagEnabled(Flag flag) const { return (flags_ & flag) > 0; }
 
+bool Connection::CanMigrate() const {
+  return !is_running_                                                    // reading or writing
+         && !IsFlagEnabled(redis::Connection::kCloseAfterReply)          // close after reply
+         && saved_current_command_ == nullptr                            // not executing blocking command like BLPOP
+         && subscribe_channels_.empty() && subscribe_patterns_.empty();  // not subscribing any channel
+}
+
 void Connection::SubscribeChannel(const std::string &channel) {
   for (const auto &chan : subscribe_channels_) {
     if (channel == chan) return;
@@ -296,8 +304,6 @@ void Connection::ExecuteCommands(std::deque<CommandTokens> *to_process_cmds) {
   Config *config = srv_->GetConfig();
   std::string reply, password = config->requirepass;
 
-  has_running_command_ = true;
-  MakeScopeExit([this] { has_running_command_ = false; });
   while (!to_process_cmds->empty()) {
     auto cmd_tokens = to_process_cmds->front();
     to_process_cmds->pop_front();

src/server/redis_connection.h

@@ -111,7 +111,6 @@ class Connection : public EvbufCallbackBase<Connection> {
   Worker *Owner() { return owner_; }
   void SetOwner(Worker *new_owner) { owner_ = new_owner; };
   int GetFD() { return bufferevent_getfd(bev_); }
-  bool HasRunningCommand() const { return has_running_command_; }
   evbuffer *Input() { return bufferevent_get_input(bev_); }
   evbuffer *Output() { return bufferevent_get_output(bev_); }
   bufferevent *GetBufferEvent() { return bev_; }
@@ -120,6 +119,7 @@ class Connection : public EvbufCallbackBase<Connection> {
   void RecordProfilingSampleIfNeed(const std::string &cmd, uint64_t duration);
   void SetImporting() { importing_ = true; }
   bool IsImporting() const { return importing_; }
+  bool CanMigrate() const;
 
   // Multi exec
   void SetInExec() { in_exec_ = true; }
@@ -160,7 +160,7 @@ class Connection : public EvbufCallbackBase<Connection> {
   Server *srv_;
   bool in_exec_ = false;
   bool multi_error_ = false;
-  std::atomic<bool> has_running_command_ = false;
+  std::atomic<bool> is_running_ = false;
   std::deque<redis::CommandTokens> multi_cmds_;
 
   bool importing_ = false;

src/server/worker.cc

@@ -360,10 +360,15 @@ redis::Connection *Worker::removeConnection(int fd) {
 // blocked on a key or stream.
 void Worker::MigrateConnection(Worker *target, redis::Connection *conn) {
   if (!target || !conn) return;
+
+  auto bev = conn->GetBufferEvent();
+  // disable read/write event to prevent the connection from being processed during migration
+  bufferevent_disable(bev, EV_READ | EV_WRITE);
   // We cannot migrate the connection if it has a running command
   // since it will cause data race since the old worker may still process the command.
-  if (conn->HasRunningCommand()) {
-    // don't need to close the connection since destroy worker thread will close it
+  if (!conn->CanMigrate()) {
+    // Need to enable read/write event again since we disabled them before
+    bufferevent_enable(bev, EV_READ | EV_WRITE);
     return;
   }
 
@@ -373,7 +378,6 @@ void Worker::MigrateConnection(Worker *target, redis::Connection *conn) {
     conn->Close();
     return;
   }
-  auto bev = conn->GetBufferEvent();
   bufferevent_base_set(target->base_, bev);
   conn->SetCB(bev);
   bufferevent_enable(bev, EV_READ | EV_WRITE);