Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 13 Oct 2001 11:44:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 13 Oct 2001 11:44:42 -0400 Received: from [212.21.93.146] ([212.21.93.146]:42883 "EHLO kushida.jlokier.co.uk") by vger.kernel.org with ESMTP id ; Sat, 13 Oct 2001 11:44:28 -0400 Date: Sat, 13 Oct 2001 17:44:27 +0200 From: Jamie Lokier To: Paul Menage Cc: Christoph Rohland , linux-kernel@vger.kernel.org Subject: Re: [PATCH][RFC] Pollable /proc// - avoid SIGCHLD/poll() races Message-ID: <20011013174427.D20499@kushida.jlokier.co.uk> In-Reply-To:

Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: ; from pmenage@ensim.com on Thu, Oct 04, 2001 at 02:31:40AM -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Paul Menage wrote: > >or use sigsetjmp/siglongjmp > > Yes, that would probably solve the situation in question, provided that > siglongjmp() is portably safe. siglongjmp() or longjmp() should be safe on all unix systems, though not others. You have to be careful: if you receive a SIGCHLD _while_ handling a SIGINT (or another signal), you must not siglongjmp() out of the inner handler. The simplest way get this right is to make sure that the other signal handlers mask out SIGCHLD while they are running. You will need to use sigaction() for this, and that isn't as portable as siglongjmp(). > (A comment on LKML in the past suggested that it's not safe on > cygwin, for example.) I wrote that comment. At least two versions of cygwin crash when you call siglongjmp() from a signal handler inside select(). Unfortunately I did not distill a reliable test for this, to check later versions of cygwin. However, given that that _should_ work, I don't think you can rely write() working under these conditions in cygwin either. So don't choose a pipe just for this reason. > >Both would be portable and not special to child handling. > > One advantage of the pollable /proc/, (when combined with > do_notify_parent() waking tsk->exit_chldwait) is that any process can > check for the exit of any other process (not just direct children) in a > select()/poll() call. Well, pollable /proc/ is not portable at all. If you are going to use something linux specific, you may as well use pselect() which is portable to a number of modern unix systems. enjoy, -- Jamie - 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/