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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 0F798CA9EA0 for ; Sun, 20 Oct 2019 12:33:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA97D21927 for ; Sun, 20 Oct 2019 12:33:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=colorfullife-com.20150623.gappssmtp.com header.i=@colorfullife-com.20150623.gappssmtp.com header.b="QLbN55Fb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726385AbfJTMdV (ORCPT ); Sun, 20 Oct 2019 08:33:21 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:44774 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726295AbfJTMdV (ORCPT ); Sun, 20 Oct 2019 08:33:21 -0400 Received: by mail-wr1-f67.google.com with SMTP id z9so10787307wrl.11 for ; Sun, 20 Oct 2019 05:33:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=colorfullife-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=nxh5NV2AmNEFTz2ISM0chZMRRCcl5MowgBSMrJDBPQA=; b=QLbN55FbN+5aCDgcspedlQWEDht7Bomwc6LjA6JcVmV46rYLS+OCOkZvnNDEMy5uik kgUUwW2V2WSnWxgwcDLuFshRhfCEMouRtPSRK67oZYOpGsiQakyI6tSdhDG3mKE4RNkR Qo92Scq4vX9EP0bPnxb+Z7RxKFCQKnsAm5r3HwueysyQ2cV5agXZXZKDHmZp+9vZs4+K TE5DcQD/zSd6aSEKotpzC8jOX5SPhJ1B1LPlaTQLJ2TMEBItd4y+MuG9pM8C9R7UkHrP nG0NHxWUEYVEoyZAOGq0X2WMI1qL5rZdoI5RjSBHPeij2ldmLjqyAtM8hsfYVRzwgVZo 3OzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=nxh5NV2AmNEFTz2ISM0chZMRRCcl5MowgBSMrJDBPQA=; b=SVO46kCVcjCZiPq4LxIxg4laKhgFTwug7WOtVcNObLOZyLX2A1oaaTk0B4jMRzPxS/ l4kZBqm8hL03UblKxw1IF3UU+eYDY77bLwojuRZrMSUByetikd72yX5r4ETNpPrVBGNw BhkvTJJmUjvr7BIEfjpdAjnnxs/mey2UNp/cIKTgJ+ukrIPsFgVEXTMBy6dZT0QatesR /WC1jGVtaUTCGEEGjrUYEPF4O0PGD/4ukj67Qboh/8A9WFkjB1Jrb0lm8kjoy8rWeFCm 5fAnWXBwYcNtKBYK/gfyp/we3ukVc5fZE4ImqrH28TaRApzUz8Q34zq2h1RWfvUZFu6e vp8w== X-Gm-Message-State: APjAAAXdj9pYojaH9BHitzArd45psmz1mxH4i/aO4gzseW0ilQcGKOWu sPzKoLOM7UIwRPvreCwY/KiRYHyIrjA= X-Google-Smtp-Source: APXvYqyTO3HhFtFuCZ3TCQvKH+VkNtZT9SzTHt8rytbwml8c1VH9rKKV/i6d/fx6ZdCfMKCxDSJd/Q== X-Received: by 2002:adf:e886:: with SMTP id d6mr16040198wrm.188.1571574798617; Sun, 20 Oct 2019 05:33:18 -0700 (PDT) Received: from linux.fritz.box (p200300D99703FC00226A5479D1389944.dip0.t-ipconnect.de. [2003:d9:9703:fc00:226a:5479:d138:9944]) by smtp.googlemail.com with ESMTPSA id t13sm15065400wra.70.2019.10.20.05.33.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 20 Oct 2019 05:33:17 -0700 (PDT) From: Manfred Spraul To: LKML , Davidlohr Bueso , Waiman Long Cc: 1vier1@web.de, Andrew Morton , Peter Zijlstra , Manfred Spraul , Will Deacon Subject: [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation Date: Sun, 20 Oct 2019 14:33:01 +0200 Message-Id: <20191020123305.14715-2-manfred@colorfullife.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20191020123305.14715-1-manfred@colorfullife.com> References: <20191020123305.14715-1-manfred@colorfullife.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When adding the _{acquire|release|relaxed}() variants of some atomic operations, it was forgotten to update Documentation/memory_barrier.txt: smp_mb__{before,after}_atomic() is now intended for all RMW operations that do not imply a memory barrier. 1) smp_mb__before_atomic(); atomic_add(); 2) smp_mb__before_atomic(); atomic_xchg_relaxed(); 3) smp_mb__before_atomic(); atomic_fetch_add_relaxed(); Invalid would be: smp_mb__before_atomic(); atomic_set(); In addition, the patch splits the long sentence into multiple shorter sentences. Fixes: 654672d4ba1a ("locking/atomics: Add _{acquire|release|relaxed}() variants of some atomic operations") Signed-off-by: Manfred Spraul Acked-by: Waiman Long Cc: Davidlohr Bueso Cc: Peter Zijlstra Cc: Will Deacon --- Documentation/memory-barriers.txt | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 1adbb8a371c7..fe43f4b30907 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1873,12 +1873,16 @@ There are some more advanced barrier functions: (*) smp_mb__before_atomic(); (*) smp_mb__after_atomic(); - These are for use with atomic (such as add, subtract, increment and - decrement) functions that don't return a value, especially when used for - reference counting. These functions do not imply memory barriers. - - These are also used for atomic bitop functions that do not return a - value (such as set_bit and clear_bit). + These are for use with atomic RMW functions that do not imply memory + barriers, but where the code needs a memory barrier. Examples for atomic + RMW functions that do not imply are memory barrier are e.g. add, + subtract, (failed) conditional operations, _relaxed functions, + but not atomic_read or atomic_set. A common example where a memory + barrier may be required is when atomic ops are used for reference + counting. + + These are also used for atomic RMW bitop functions that do not imply a + memory barrier (such as set_bit and clear_bit). As an example, consider a piece of code that marks an object as being dead and then decrements the object's reference count: -- 2.21.0