Fix stop gaussdb failed when init thread failed.

src/gausskernel/process/main/main.cpp

@@ -114,6 +114,7 @@ int main(int argc, char* argv[])
     PmTopMemoryContext = t_thrd.top_mem_cxt;
 
     knl_thread_init(MASTER_THREAD);
+    t_thrd.bn = NULL;
 
     t_thrd.fake_session = create_session_context(t_thrd.top_mem_cxt, 0);
     t_thrd.fake_session->status = KNL_SESS_FAKE;

src/gausskernel/process/postmaster/postmaster.cpp

@@ -10074,6 +10074,20 @@ int GaussDbThreadMain(knl_thread_arg* arg)
     /* Do this sooner rather than later... */
     IsUnderPostmaster = true; /* we are a postmaster subprocess now */
     Assert(thread_role == arg->role);
+    /*
+     * We should set bn at the beginning of this function, cause if we meet some error before set bn, then we
+     * can't set t_thrd.bn->dead_end to true(check gs_thread_exit), which will lead CleanupBackend failed.
+     * The logic of get child slot refer to PortInitialize -> read_backend_variables -> restore_backend_variables
+     */
+    int childSlot = 0;
+    if (arg != NULL) {
+        if (arg->role == RPC_WORKER) {
+            childSlot = backend_save_para.MyPMChildSlot;
+        } else {
+            childSlot = ((BackendParameters*)arg->save_para)->MyPMChildSlot;
+        }
+    }
+    t_thrd.bn = GetBackend(childSlot);
     /* Check this thread will use reserved memory or not */
     is_memory_backend_reserved(arg);
     /* Initialize the Memory Protection at the thread level */
@@ -10130,8 +10144,6 @@ int GaussDbThreadMain(knl_thread_arg* arg)
 
     PortInitialize(&port, arg);
 
-    t_thrd.bn = GetBackend(t_thrd.proc_cxt.MyPMChildSlot);
-
     /* We don't need read GUC variables */
     if (!FencedUDFMasterMode) {
         /* Read in remaining GUC variables */

src/gausskernel/process/threadpool/knl_thread.cpp

@@ -1478,11 +1478,11 @@ void knl_thread_mot_init()
 
 void knl_thread_init(knl_thread_role role)
 {
+    /* doesn't init t_thrd.bn, check GaussDbThreadMain for detail */
     t_thrd.role = role;
     t_thrd.subrole = NO_SUBROLE;
     t_thrd.proc = NULL;
     t_thrd.pgxact = NULL;
-    t_thrd.bn = NULL;
     t_thrd.myLogicTid = 10000;
     t_thrd.fake_session = NULL;
     t_thrd.threadpool_cxt.reaper_dead_session = false;