600k左右的图片就没办法上传了，请问咋修改

1. 2018/10/20 23:02:00 [error] 16976#0: *1 upstream prematurely closed connection while reading response header from upstream, client: 115.60.5.81, server: weixin.kangbanmeijia.com, request: "POST /admin/system/upload.html HTTP/2.0", upstream: "fastcgi://unix:/tmp/php-cgi-71.sock:", host: "weixin.kangbanmeijia.com", referrer: "https://weixin.kangbanmeijia.com/admin/cases/addcase.html"

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自己做的网站后台，上传图片，600k左右的图片上传不上去，500k左右的就可以，  查到说是upstream prematurely closed connection while reading response header from upstream  的问题
不知道咋修改啊，还请指教啊