infinite loop until server fails in upstream module with round robin

[unixant@…]

I use nginx as a load balancing for backend web server.
if this upstream has n servers,and m backup servers,and the n servers are not available(Connection refused),round robin will try n*max_fails times to connect to the n servers。but if there is no backup servers,round robin only try n times to the n servers.
such as:

upstream bdbk {

#no program listen on 8081,8082

server 127.0.0.1:8081 max_fails=3 fail_timeout=10s;
server 127.0.0.1:8082 max_fails=3 fail_timeout=10s;

server 127.0.0.1:8083 max_fails=3 fail_timeout=10s backup;
server 127.0.0.1:8084 max_fails=3 fail_timeout=10s backup;

}

if i make a request,upstream try 6(n*max_fails) to connect to 8081 8082 , then round robin try to connect to backup server.

if there is no backup servers。nginx only try 2(n) connect to 8081 8082。

[Maxim Dounin]

This a variation of #47.