From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95A33C43441 for ; Thu, 22 Nov 2018 15:21:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 60C4C20684 for ; Thu, 22 Nov 2018 15:21:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 60C4C20684 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437665AbeKWCBE (ORCPT ); Thu, 22 Nov 2018 21:01:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42594 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730517AbeKWCBE (ORCPT ); Thu, 22 Nov 2018 21:01:04 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D093E31256BE; Thu, 22 Nov 2018 15:21:15 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-116-170.ams2.redhat.com [10.36.116.170]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 507F85C21E; Thu, 22 Nov 2018 15:21:10 +0000 (UTC) From: Florian Weimer To: Rich Felker Cc: Mathieu Desnoyers , carlos , Joseph Myers , Szabolcs Nagy , libc-alpha , Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Will Deacon , Dave Watson , Paul Turner , linux-kernel , linux-api Subject: Re: [RFC PATCH v4 1/5] glibc: Perform rseq(2) registration at nptl init and thread creation References: <20181121183936.8176-1-mathieu.desnoyers@efficios.com> <20181122143603.GD23599@brightrain.aerifal.cx> <782067422.9852.1542899056778.JavaMail.zimbra@efficios.com> <87a7m1ywni.fsf@oldenburg.str.redhat.com> <20181122151710.GF23599@brightrain.aerifal.cx> Date: Thu, 22 Nov 2018 16:21:02 +0100 In-Reply-To: <20181122151710.GF23599@brightrain.aerifal.cx> (Rich Felker's message of "Thu, 22 Nov 2018 10:17:10 -0500") Message-ID: <875zwpyw81.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Thu, 22 Nov 2018 15:21:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Rich Felker: > On Thu, Nov 22, 2018 at 04:11:45PM +0100, Florian Weimer wrote: >> * Mathieu Desnoyers: >> >> > Thoughts ? >> > >> > /* Unregister rseq TLS from kernel. */ >> > if (has_rseq && __rseq_unregister_current_thread ()) >> > abort(); >> > >> > advise_stack_range (pd->stackblock, pd->stackblock_size, (uintptr_t) pd, >> > pd->guardsize); >> > >> > /* If the thread is detached free the TCB. */ >> > if (IS_DETACHED (pd)) >> > /* Free the TCB. */ >> > __free_tcb (pd); >> >> Considering that we proceed to free the TCB, I really hope that all >> signals are blocked at this point. (I have not checked this, though.) >> >> Wouldn't this address your concern about access to the rseq area? > > I'm not familiar with glibc's logic here, but for other reasons, I > don't think freeing it is safe until the kernel task exit futex (set > via clone or set_tid_address) has fired. I would guess __free_tcb just > sets up for it to be reclaimable when this happens rather than > immediately freeing it for reuse. Right, but in case of user-supplied stacks, we actually free TLS memory at this point, so signals need to be blocked because the TCB is (partially) gone after that. Thanks, Florian