keep got warning message with openresty

[rttw]

lua code:

local lfs=require("lfs")
lfs.xxxxxx

openresty got warnning message like :
2022/03/04 09:37:52 [warn] 13025#13025: *37 [lua] _G write guard:12: writing a global Lua variable ('lfs') which may lead to race conditions between concurrent requests, so prefer the use of 'local' variables
stack traceback:
[C]: at 0x7fbb0d0dda20
[C]: in function 'require'