HTTP3 php-fpm fastcgi_pass 500 problems

[Ryan Gould]

hello awesome nginx developers,

i am having some odd behavior issues when in http3 / quic mode.

i am using a completely-up-to-date nginx-quic build on a debian 9 box.

my nginx php-fpm configuration has been solid and unchanging for years 
and years.

if i disable http3 / quic, things work great in http2 mode.  if i enable 
http3 / quic mode, something is causing all php7.3-fpm pages to generate 
"500 Internal Server Error" pages.  static html pages render perfectly.

despite adding all the extra log arguments to nginx and to php7.3-fpm 
(display_errors and the rest) i am only seeing the following in the 
nginx error log:

2020/10/10 21:19:47 [alert] 10614#0: *37 epoll_ctl(1, -1) failed (9: Bad 
file descriptor), client: X.X.X, server: example.com, request: "GET 
/php_test_page HTTP/3"

there is nothing to be seen in any other browser or server log.  the 
server does send the default / implied favicon.ico perfectly.  the php 
test page is only a phpinfo() command.

i have always used the fastcgi_pass socket setup, but i have also tried 
the port version (same problem).

the same exact thing happens when i try it with a completely-up-to-date 
nginx-quiche build on a different server.

i have not had much luck tracking down info on "epoll_ctl".

any thoughts or suggestions?

if i can help with logs, please let me know.