Sometimes on my CentOS servers with Apache 2 + mod_ssl, Apache stops responding to requests made through HTTPS. The SSL connection and handshake is successfull (I tested it with openssl s_client), but Apache doesn't send any data to the socket after I manually send a HTTP request. At the same time, HTTP is working perfectly. For instance, even a broken request with just "GET /" instantly throws a "400 Bad Request" error over HTTP whereas I don't get any answer over SSL.
apache2ctl graceful doesn't solve the problem, but apache2ctl restart does. The number of open TCP connections to Apache is normal, CPU and memory are OK. apache2ctl fullstatus shows a lot of "reading data" lines.
Any idea ?