Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 17 Nov 2002 22:33:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 17 Nov 2002 22:33:59 -0500 Received: from cpe-24-221-190-179.ca.sprintbbd.net ([24.221.190.179]:40066 "EHLO myware.akkadia.org") by vger.kernel.org with ESMTP id ; Sun, 17 Nov 2002 22:33:58 -0500 Message-ID: <3DD86146.6050207@redhat.com> Date: Sun, 17 Nov 2002 19:40:54 -0800 From: Ulrich Drepper User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3a) Gecko/20021114 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jamie Lokier CC: Linus Torvalds , Ingo Molnar , Luca Barbieri , Kernel Mailing List Subject: Re: [patch] threading fix, tid-2.5.47-A3 References:

<20021118014612.GA2483@bjl1.asuk.net> In-Reply-To: <20021118014612.GA2483@bjl1.asuk.net> X-Enigmail-Version: 0.65.4.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2358 Lines: 52 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Jamie Lokier wrote: > The race condition which Ulrich brought up, which requires > CLONE_CHILD_SETTID to be used without CLONE_PARENT_SETTID, only occurs > when using the same address to store the tid of the forked child as > the parent's tid address. In other words, it's a user space error. > (Please correct me if I'm mistaken, Ulrich). It's not an error. It the very basic concept of always having a correct thread descriptor. A process created with fork() from an MT app is different from one created with fork() from a single threaded app. In the latter case the thread descriptors are not used and can contain garbage. In the former case the descriptor better be correct all the time. It basically the same problem as with setting the TLS "register". clone() get the CLONE_TLS flag because the child and parent have (potentially) different TLS address and it is not possible to set the value before the fork() call (since the parent would have the wrong value for some time) nor after the fork() (since then there would be a window for a signal to arrive for an uninitialized thread). > Finally, it would be kinder to everyone if CLONE_SETTID stored the > child's tid in _both_ the parent and child address spaces, atomically > w.r.t. debuggers. Yes, but then clone still has to get two addresses. In case of the fork() implementation the parent's TID value must not be overwritten while the child's TID value is at exactly the same virtual address as the value in the parent. I've no problem with requiring the value always to be written (the pointer can be to a scratch object) but there must be two pointer parameters for that. - -- - --------------. ,-. 444 Castro Street Ulrich Drepper \ ,-----------------' \ Mountain View, CA 94041 USA Red Hat `--' drepper at redhat.com `--------------------------- -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (GNU/Linux) iD8DBQE92GFG2ijCOnn/RHQRAjQSAKCIRuhc1wgZy1PFS+waFapXRYqGjACgt6Bn T2uKMpj7gHJedPzXxQ5EjoM= =0C7c -----END PGP SIGNATURE----- - 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/