ngx_http_upstream_dynamic_resolve_servers.diff

diff --git a/ngx_http_upstream_dynamic_resolve_servers.c b/ngx_http_upstream_dynamic_resolve_servers.c
index 62ba520..48ec4eb 100644
--- a/ngx_http_upstream_dynamic_resolve_servers.c
+++ b/ngx_http_upstream_dynamic_resolve_servers.c
@@ -640,27 +640,30 @@ reinit_upstream:
 
     pool_queue = &dynamic_server->pool_queue;
 
-    ngx_log_debug(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
+    ngx_log_error(NGX_LOG_INFO, ngx_cycle->log, 0,
                   "upstream-dynamic-servers: server '%V' pool_queue_len is %i "
                   "before insert",
                   &dynamic_server->host, dynamic_server->pool_queue_len);
 
-    for (p = pool_queue->next, n = p->next; p != pool_queue;
-         p = n, n = n->next)
+    for (p = pool_queue->next, n = p->next; p != pool_queue && dynamic_server->pool_queue_len > 0;
+         p = n,
+        n = n->next)
     {
         index++;
         tmp_node = ngx_queue_data(
             p, ngx_http_upstream_dynamic_resolve_server_pool_node_t, queue);
+
         if (tmp_node->refer_num == 0)
         {
             ngx_queue_remove(p);
-
             ngx_log_debug(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
                           "upstream-dynamic-servers: server '%V' %ith pool "
                           "will be destoried",
                           &dynamic_server->host, index);
-
-            ngx_destroy_pool(tmp_node->pool);
+            if (tmp_node->pool)
+            {
+                ngx_destroy_pool(tmp_node->pool);
+            }
             dynamic_server->pool_queue_len--;
         }
     }