PHP-FPM smooth restart causes nginx error, what is the problem?

Question

Smoothly restart php-fpm through kill -USR2 operation
Theoretically, requests to Nginx should be lossless, but there is still an error_log during the restart

recv() failed (104: Connection reset by peer) while reading response header from upstream

Answer 1

Look at the logs of php-fpm,
Post the command you used to execute kill -USR2
Also which lines of php-fpm.conf were modified