Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755724AbYAXX5m (ORCPT ); Thu, 24 Jan 2008 18:57:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751691AbYAXX5e (ORCPT ); Thu, 24 Jan 2008 18:57:34 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:50922 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751482AbYAXX5d (ORCPT ); Thu, 24 Jan 2008 18:57:33 -0500 X-AuthUser: davidel@xmailserver.org Date: Thu, 24 Jan 2008 15:57:31 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Pierre Habouzit cc: Linux Kernel Mailing List Subject: Re: epoll and shared fd's In-Reply-To: <20080124084001.GB7356@artemis.madism.org> Message-ID: References: <20080118134318.GD9607@artemis.madism.org> <20080124084001.GB7356@artemis.madism.org> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1870 Lines: 52 On Thu, 24 Jan 2008, Pierre Habouzit wrote: > On Fri, Jan 18, 2008 at 09:10:18PM +0000, Davide Libenzi wrote: > > On Fri, 18 Jan 2008, Pierre Habouzit wrote: > > > > > Hi, > > > > > > I just came across a strange behavior of epoll that seems to > > > contradict the documentation. Here is what happens: > > > > > > * I have two processes P1 and P2, P1 accept()s connections, and send the > > > resulting file descriptors to P2 through a unix socket. > > > > > > * P2 registers the received socket in his epollfd. > > > > > > [time passes] > > > > > > * P2 is done with the socket and closes it > > > > > > * P2 gets events for the socket again ! > > > > > > > > > Though the documentation says that if a process closes a file > > > descriptor, it gets unregistered. And yes I'm sure that P2 doens't dup() > > > the file descriptor. Though (because of a bug) it was still open in > > > P1[0], hence the referenced socket still live at the kernel level. > > > > > > Of course the userland workaround is to force the EPOLL_CTL_DEL before > > > the close, which I now do, but costs me a syscall where I wanted to > > > spare one :| > > > > For epoll, a close is when the kernel file* is released (that is, when all > > its instances are gone). > > We could put a special handling in filp_close(), but I don't think is a > > good idea, and we're better live with the current behaviour. > > Okay, maybe updating the linux manpages to be more clear about that is > the way to go then. Thanks Sure. I'll send Michael Kerrisk and updated statement for the A6 answer in the epoll man page. - Davide -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/