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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F9A8C4332F for ; Mon, 17 Oct 2022 14:53:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230206AbiJQOxS (ORCPT ); Mon, 17 Oct 2022 10:53:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229969AbiJQOxJ (ORCPT ); Mon, 17 Oct 2022 10:53:09 -0400 Received: from mail-ed1-x52f.google.com (mail-ed1-x52f.google.com [IPv6:2a00:1450:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86CFC67C99 for ; Mon, 17 Oct 2022 07:53:00 -0700 (PDT) Received: by mail-ed1-x52f.google.com with SMTP id a67so16368678edf.12 for ; Mon, 17 Oct 2022 07:53:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=OhVV/J8FqMZJSl3JLrYPvHzM0WqDA/VczwIl8A3roZY=; b=ogcKAH8XXSikjmWWNA8FA8ylFT1NMJBrvD1RUcvZWQm53rDA4FtXlvNMZIVaSTYQ4M +qDz32Mm1JI3x4O4Ta0CjRyBgsZWeluHSnvgFZGvIkLd4qUNp7V8PrOnOjvUOhYSY8L/ OYDjRXUxmULH6fXf3A1wGOCe/PBgEfInhwihJgSFXN2wOsY8JgAnezknwog6io8H7LAh QWIS+4yiTgS3chhDacf7LfeBd/r96CaHWGz7xM1vBOKUw++sMO6uEpRlhXV3nTFLyLa/ /xkdXZYQcc99OZtmnlMq8D6GkMbPjAGVRobdqno07ubP73j088+7Ojwh+OOr9CiGPUMC Z6Fw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=OhVV/J8FqMZJSl3JLrYPvHzM0WqDA/VczwIl8A3roZY=; b=TPzNN3VDuaXS4lDvVzzBg3GHbEvsKMwSNkZBqOv79o5cS9DaGfVXLFn9j1DYd7gQwE N/aw5vc8r3c6SFT7gepArqxchDJvN1SSZYezS7kPKRzxKHC6kniWk+IhoAj1Sg5695In bAlXmcadQ2eJfQMl85BzbatfixRgXOiHPKSSL4VhbEZlGF1WlLT+kC96m15ZQlKPVLa8 RJncLwnehL2brSWNHFxjFftG/fn6uBazclTFEZVNUeD1Og9LGo1GQJEwKFZ2BgpxzudZ 2s1MIlfyPwhllIWmQYu++YyrRbzlXaTocj0/xBYHnOXN3hQCFHrP9FTmnWFi3fi8iOks cUgw== X-Gm-Message-State: ACrzQf1P8VHccTTqv5glQ4cc8tBt37Jt0CohHkBTIV0ilU0ahTxbEsyX O2l1fdIu2T9wyFOQx0fKcclf4mw2sRwMZA== X-Google-Smtp-Source: AMsMyM4wjpBDWpJSk020Zp8p8/I2eF2XTpW+sczRo9STwoPma9N/cCIxw3UXvVpCdpBEFih9qi0cfA== X-Received: by 2002:a05:6402:d0b:b0:458:a244:4e99 with SMTP id eb11-20020a0564020d0b00b00458a2444e99mr10679974edb.46.1666018378864; Mon, 17 Oct 2022 07:52:58 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id ss5-20020a170907038500b0073c80d008d5sm6084809ejb.122.2022.10.17.07.52.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Oct 2022 07:52:58 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Andrew Morton Subject: [PATCH] llist: Avoid extra memory read in llist_add_batch Date: Mon, 17 Oct 2022 16:52:26 +0200 Message-Id: <20221017145226.4044-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org try_cmpxchg implicitly assigns old head->first value to "first" when cmpxchg fails. There is no need to re-read the value in the loop. Cc: Andrew Morton Signed-off-by: Uros Bizjak --- lib/llist.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/llist.c b/lib/llist.c index 7d78b736e8af..6e668fa5a2c6 100644 --- a/lib/llist.c +++ b/lib/llist.c @@ -26,10 +26,10 @@ bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, struct llist_head *head) { - struct llist_node *first; + struct llist_node *first = READ_ONCE(head->first); do { - new_last->next = first = READ_ONCE(head->first); + new_last->next = first; } while (!try_cmpxchg(&head->first, &first, new_first)); return !first; -- 2.37.3