Possible infinite loop in mod_proxy

[Chris Monson]

I apologize if this is the wrong forum for this information. I started with the mod_proxy dev list, and they suggested that the problem was probably with Apache's filter code, and that I should post the issue here.

I have been working with mod_proxy under Apache 2.0.44 and have been having some problems.

The basic setup is using the worker MPM and is as follows:

Listen 8008
<VirtualHost *:8008>
ServerName myproxy.mydomain.mytld
DocumentRoot "/unnecessary/path/to/files"

ProxyRequests On
ProxyPreserveHost on
ProxyReceiveBufferSize 4096
ProxyTimeout 20
ProxyVia off
</VirtualHost>

In my browser, I set the proxy to be myproxy.mydomain.mytld at port 8008. Things seem to work all right for simple requests. However, requesting a really messy page like "www.cnn.com" causes some interesting problems. (For bug duplication purposes, I am currently using Mozilla 1.3a, but this has been duplicated on various versions of IE, as well).

After making the request to www.cnn.com, Apache must be forcefully restarted in order serve any other requests reliably. Request threads do not appear to want to give up their connection to the internet once the request is completed. An ethereal dump indicates that Apache is still sending TCP traffic to the destination server. An endless stream of ACK packets is sent to the destination server until Apache is forcefully restarted. I have verified that it is not the browser that is doing this.

Additionally, the problem is greatly alleviated (though not eradicated) by turning off keepalive in the proxy code or in the conf file. I can make several requests reliably with keepalive turned off, but eventually the server gets hung up. It doesn't send an endless stream of packets to the destination server without keepalive, however.

When the server hangs like that, a restart indicates that the children must receive a SIGKILL, but it never finishes restarting. If I run

$ apachectl stop

then it wakes up and starts sending data again, strangely. This appears to me to be some kind of a deadly embrace in the worker code, but that is a very preliminary assumption and has not yet been tested. It just feels like that kind of a problem since attempting to kill the process seems to wake things up (mostly) again.

I checked the bug database for this kind of problem, and it appears that in October of last year a bug was submitted that may be related, dealing with a keepalive-related memory leak in Apache. I believe that bug to be somewhat related, though not quite the same thing I am experiencing. What I get is a completely frozen server.

C