From patchwork Thu Mar 11 17:54:04 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jonathan Wakely X-Patchwork-Id: 1451431 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org (client-ip=8.43.85.97; helo=sourceware.org; envelope-from=gcc-patches-bounces@gcc.gnu.org; receiver=) Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=gcc.gnu.org header.i=@gcc.gnu.org header.a=rsa-sha256 header.s=default header.b=LMQURQPr; dkim-atps=neutral Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 4DxGmR6DgWz9sS8 for ; Fri, 12 Mar 2021 04:54:31 +1100 (AEDT) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id A152A3897817; Thu, 11 Mar 2021 17:54:18 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A152A3897817 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1615485258; bh=A4riwKjOoZqEfTbbY04oVQQxQ8xM69MMkUFOd9eo138=; h=Date:To:Subject:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:From; b=LMQURQPrttVnvTb4/8PaN7piNUrXTU0mbTcIBR9WkeejKf/GrHQPVBnvLfDtlicZF HB165ka5r1NyzZ0s8ojHw7b0PtCR/WbtHGD2AuApeldEwjnyqAuxeeSd5py1hqqwtQ 5mYmGnG5n5sS2bLOE6oIs8n28sg+vAPXzKGIo09I= X-Original-To: gcc-patches@gcc.gnu.org Delivered-To: gcc-patches@gcc.gnu.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id 53E683897814 for ; Thu, 11 Mar 2021 17:54:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 53E683897814 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-455-9x6_g28jNjqXsGohE8FJbQ-1; Thu, 11 Mar 2021 12:54:06 -0500 X-MC-Unique: 9x6_g28jNjqXsGohE8FJbQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AF0B918460E0; Thu, 11 Mar 2021 17:54:05 +0000 (UTC) Received: from localhost (unknown [10.33.36.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id 562615DDAD; Thu, 11 Mar 2021 17:54:05 +0000 (UTC) Date: Thu, 11 Mar 2021 17:54:04 +0000 To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [committed] libstdc++: Use acq_rel memory ordering [PR 99537] Message-ID: MIME-Version: 1.0 X-Clacks-Overhead: GNU Terry Pratchett X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline X-Spam-Status: No, score=-14.3 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=unavailable autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Jonathan Wakely via Gcc-patches From: Jonathan Wakely Reply-To: Jonathan Wakely Errors-To: gcc-patches-bounces@gcc.gnu.org Sender: "Gcc-patches" As Lewis Baker wrote in the PR: > The 'fetch_sub()' operation in _M_release_ownership() should be using > memory_order::acq_rel instead of memory_order::release. The use of > 'release' only is insufficient as it does not synchronise with any > corresponding 'acquire' operation. > With the current implementation, it's possible that a prior write to > one of the _M_value or _M_head data-members by a thread releasing the > second-to-last reference might not be visible to another thread that > releases the last reference and frees the memory, resulting in > potential write to freed memory. This simply changes the memory order to acq_rel as suggested. libstdc++-v3/ChangeLog: PR libstdc++/99537 * include/std/stop_token (_Stop_state_t::_M_release_ownership): Use acq_rel memory ordering. Tested powerpc64le-linux. Committed to trunk. commit 15825b17cf3fbf28181c51fe94a2898f448f915c Author: Jonathan Wakely Date: Thu Mar 11 16:44:57 2021 libstdc++: Use acq_rel memory ordering [PR 99537] As Lewis Baker wrote in the PR: > The 'fetch_sub()' operation in _M_release_ownership() should be using > memory_order::acq_rel instead of memory_order::release. The use of > 'release' only is insufficient as it does not synchronise with any > corresponding 'acquire' operation. > With the current implementation, it's possible that a prior write to > one of the _M_value or _M_head data-members by a thread releasing the > second-to-last reference might not be visible to another thread that > releases the last reference and frees the memory, resulting in > potential write to freed memory. This simply changes the memory order to acq_rel as suggested. libstdc++-v3/ChangeLog: PR libstdc++/99537 * include/std/stop_token (_Stop_state_t::_M_release_ownership): Use acq_rel memory ordering. diff --git a/libstdc++-v3/include/std/stop_token b/libstdc++-v3/include/std/stop_token index 83905f6525f..fffc215d2a8 100644 --- a/libstdc++-v3/include/std/stop_token +++ b/libstdc++-v3/include/std/stop_token @@ -185,7 +185,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION void _M_release_ownership() noexcept { - if (_M_owners.fetch_sub(1, memory_order::release) == 1) + if (_M_owners.fetch_sub(1, memory_order::acq_rel) == 1) delete this; }