From patchwork Mon Jul 1 11:42:28 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wolfgang Bumiller X-Patchwork-Id: 1954643 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@legolas.ozlabs.org Authentication-Results: legolas.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=patchwork.ozlabs.org) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by legolas.ozlabs.org (Postfix) with ESMTPS id 4WCPLY05BWz1xpN for ; Mon, 1 Jul 2024 21:43:16 +1000 (AEST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sOFQp-0004om-DT; Mon, 01 Jul 2024 07:42:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sOFQi-0004nn-Pd for qemu-devel@nongnu.org; Mon, 01 Jul 2024 07:42:45 -0400 Received: from proxmox-new.maurer-it.com ([94.136.29.106]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sOFQg-0006hS-2Q for qemu-devel@nongnu.org; Mon, 01 Jul 2024 07:42:44 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id CFCF745F18; Mon, 1 Jul 2024 13:42:30 +0200 (CEST) From: Wolfgang Bumiller To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Stefan Weil , Kevin Wolf , Hanna Reitz , Stefan Hajnoczi , Fam Zheng Subject: [PATCH 0/2] change some odd-looking atomic uses Date: Mon, 1 Jul 2024 13:42:28 +0200 Message-Id: <20240701114230.193307-1-w.bumiller@proxmox.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Received-SPF: pass client-ip=94.136.29.106; envelope-from=w.bumiller@proxmox.com; helo=proxmox-new.maurer-it.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org I spotted the weird-looking pattern of: atomic_set(atomic_load() N) in a few palces and one variable in the graph-lock code which was used with atomics except for a single case, which also seemed suspicious. I'm not sure if there are any known compiler-optimizations or ordering semantics already ensuring that these operations are indeed working correctly atomically, so I thought I'd point them out and ask about it by sending patches. In patch 2 the ordering is changed (see the note in its mail) Wolfgang Bumiller (2): graph-lock: make sure reader_count access is atomic atomics: replace fetch-use-store with direct atomic operations block/graph-lock.c | 8 +++----- util/aio-posix.c | 3 +-- util/aio-win32.c | 3 +-- util/async.c | 2 +- 4 files changed, 6 insertions(+), 10 deletions(-)