Panic on recursive calls to luaRedisGenericCommand().

Related to issue #2302.

src/scripting.c

@@ -213,11 +213,22 @@ int luaRedisGenericCommand(lua_State *lua, int raise_error) {
     static int argv_size = 0;
     static robj *cached_objects[LUA_CMD_OBJCACHE_SIZE];
     static size_t cached_objects_len[LUA_CMD_OBJCACHE_SIZE];
+    static int inuse = 0;   /* Recursive calls detection. */
+
+    /* By using Lua debug hooks it is possible to trigger a recursive call
+     * to luaRedisGenericCommand(), which normally should never happen.
+     * To make this function reentrant is futile and makes it slower, but
+     * we should at least detect such a misuse, and abort. */
+    if (inuse) {
+        redisPanic("luaRedisGenericCommand() recursive call detected. Are you doing funny stuff with Lua debug hooks?");
+    }
+    inuse++;
 
     /* Require at least one argument */
     if (argc == 0) {
         luaPushError(lua,
             "Please specify at least one argument for redis.call()");
+        inuse--;
         return 1;
     }
 
@@ -272,6 +283,7 @@ int luaRedisGenericCommand(lua_State *lua, int raise_error) {
         }
         luaPushError(lua,
             "Lua redis() command arguments must be strings or integers");
+        inuse--;
         return 1;
     }
 
@@ -408,8 +420,10 @@ cleanup:
          * return the plain error. */
         lua_pushstring(lua,"err");
         lua_gettable(lua,-2);
+        inuse--;
         return lua_error(lua);
     }
+    inuse--;
     return 1;
 }