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Message-ID: <F4F95B37FBE5E644988011E91104C7620A8F199A6D@MAIL1.tekelec.com> Date: Wed, 9 Jan 2013 09:35:30 -0500 From: "Hassink, Brian" <Brian.Hassink@...elec.com> To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: epoll and listener sockets I have a little more information on this problem... I modified my test so that after the connection attempt is made, I force the listener to do an accept() and found that the connection is in the listener queue. As I mentioned below, the connection attempt is made a full second after the listener is added to the epoll set, so there should not be any sort of race condition occurring. -Brian -----Original Message----- From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Hassink, Brian Sent: Tuesday, January 08, 2013 5:32 PM To: linux-kernel@...r.kernel.org Subject: epoll and listener sockets $ uname -r 2.6.32-279.5.2.el6prerel6.0.0_80.23.0.x86_64 $ cat /etc/issue CentOS release 6.3 (Final) I sincerely hope this is the correct forum in which to ask about this, and apologize profusely if it is not. I have a listener socket in an epoll set, and it will occasionally fail to receive an EPOLLIN event for a connection. I have looked at a few example programs, which typically have the following sequence... 1. call socket() 2. call bind() 3. call fcntl() to make fd non-blocking 4. call epoll_ctl() to add the fd with (EPOLLET | EPOLLONESHOT | EPOLLIN) 5. call listen() 6. enter epoll_wait() loop ...where the listener socket is added to the epoll set before the epoll_wait() loop. In my application, concurrent threads are running in an epoll_wait() loop and a listener socket may be created at any time. I had initially tried this sequence... 1. call socket() 2. call bind() 3. call fcntl() to make fd non-blocking 4. call epoll_ctl() to add the fd with (EPOLLET | EPOLLONESHOT | EPOLLIN) 5. call listen() ...but often received an EPOLLHUP event because of a concurrent epoll_wait() call between step 4 and 5. So I switched the sequence to... 1. call socket() 2. call bind() 3. call fcntl() to make fd non-blocking 4. call listen() 5. call epoll_ctl() to add the fd with (EPOLLET | EPOLLONESHOT | EPOLLIN) In my testing there is only one connection attempt to the listener port, so EPOLLONESHOT should not be a factor. I have also tried level-triggered with the same result. I should also note that the connection attempt is made exactly one second after the listener is created. So there isn't a race where the connection attempt is already queued before the listener is added to the epoll set. I saw that there was a recent patch for EPOLL_CTL_MOD and EPOLLONESHOT, but I don't think that is relevant here. Any thoughts on what the problem might be? Thanks in advance, Brian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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