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 B8300C4332F for ; Fri, 10 Nov 2023 18:03:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235338AbjKJSDX (ORCPT ); Fri, 10 Nov 2023 13:03:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58006 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235709AbjKJSCe (ORCPT ); Fri, 10 Nov 2023 13:02:34 -0500 Received: from mail-pl1-x62d.google.com (mail-pl1-x62d.google.com [IPv6:2607:f8b0:4864:20::62d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4FDD428B33 for ; Fri, 10 Nov 2023 02:29:41 -0800 (PST) Received: by mail-pl1-x62d.google.com with SMTP id d9443c01a7336-1cc1ee2d8dfso16988275ad.3 for ; Fri, 10 Nov 2023 02:29:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shopee.com; s=shopee.com; t=1699612181; x=1700216981; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:references:cc:to:subject :user-agent:mime-version:date:message-id:from:to:cc:subject:date :message-id:reply-to; bh=nnpoVDYUjKd3G8MoAHqwJcbkn3YvVxdpV7jnAIYRk30=; b=flxy7wLdaPIV2hoMl2P9zGsGxYIYkEugXlcX2aaDFGT5jxCiwCrJxCzCl2va13k7HM gwfvCKetAA2eRzyniXXK7i/eIcHsBDj2rkHT5EQ5rq2sFbE0xEVh9v0BjVxHG4QTkvQ4 9xSsR59t7wmRX0IUaoXyq3lPuWxORkNc8QTr+aiPXFPUAzxf6kCoIgMXm9+ke0NsRrSU ZnGlBji9Xh5g54FtDMITkBmd9YNxi11kxabJ0P/B1P/AHMxIj0iSwhfhkuGXuAmuFqat saRYyNDGcI+Qm+hqBCe2jnRFJUnxxM3bUYVXhdIyAEUBAXe7OAtrox+XhYrTdBBVj9s9 llTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699612181; x=1700216981; h=content-transfer-encoding:in-reply-to:from:references:cc:to:subject :user-agent:mime-version:date:message-id:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=nnpoVDYUjKd3G8MoAHqwJcbkn3YvVxdpV7jnAIYRk30=; b=v2rUGdNNnPkqWL6cgMeBqqxMvQIUP50OQBCvBjQbikULa7UhjST0ex+cAJtnqKgbls VnFQFHMEp8x2b4hK4bwed2G1hH4K8ivJfvmShpf4rQPnHHxNfcSCXs5saL9tWbKR9sL1 CMF3WwnTW9PAPobvl/drauCqrAes1LYZyfQ96+xPKadWnATnDCHHxV+Fqd2rS820l9is zM4loZZmQp8goITrGV7zouI6bVlO1TvrvtcsV0nMSLZLsxrBNKopfWM+t4KhO/rFDR4d iudnwIjyYdn0OT0k0DdGscoh+PaqoErO20gDftUIJ7ug+DvGEanXHpSPjVXLAOWhHgdw ascg== X-Gm-Message-State: AOJu0YzQmaUE8H9qRifKOXjrM3+FwiTjC5S/XxHa6bk83mTpU2p01k+D rDswbK1v6DsfKa0dKd3LmLriCg== X-Google-Smtp-Source: AGHT+IGaShgv4q7rmDQV4setP1Ioo5vXHwXEr6plv9+vfdgvqbtUqJnkGbGK9nhBqlaF35N2CKkeDw== X-Received: by 2002:a17:902:b284:b0:1cc:2469:f2ff with SMTP id u4-20020a170902b28400b001cc2469f2ffmr7458444plr.9.1699612180724; Fri, 10 Nov 2023 02:29:40 -0800 (PST) Received: from [10.54.24.52] ([143.92.118.3]) by smtp.gmail.com with ESMTPSA id ba2-20020a170902720200b001cc5d23275csm4983457plb.200.2023.11.10.02.29.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Nov 2023 02:29:40 -0800 (PST) Message-ID: Date: Fri, 10 Nov 2023 18:29:36 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] locking/rwsem: Remove unnessary check in rwsem_down_read_slowpath() To: Tang Yizhou Cc: Waiman Long , peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com, linux-kernel@vger.kernel.org References: <20231108105639.70088-1-haifeng.xu@shopee.com> <6da49b39-653a-1eda-2d21-1f1b50cb14f0@redhat.com> <5086cd5b-a832-4250-9927-4b300d2f611e@shopee.com> From: Haifeng Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/11/10 14:54, Tang Yizhou wrote: > On Thu, Nov 9, 2023 at 11:17 AM Haifeng Xu wrote: >> >> reader writer reader >> >> acquire >> release >> rwsem_write_trylock >> set RWSEM_WRITER_LOCKED >> rwsem_down_read_slowpath >> set owner >> >> If prev lock holder is a reader, when it releases the lock, the owner isn't cleared(CONFIG_DEBUG_RWSEMS isn't enabled). >> A writer comes and can set the RWSEM_WRITER_LOCKED bit succsessfully, then a new reader run into slow path, before >> the writer set the owner, the new reader will see that both the RWSEM_READER_OWNED bit and RWSEM_WRITER_LOCKED bit are >> set. >> > > For the above example, it won't cause a problem. When the writer > successfully sets RWSEM_WRITER_LOCKED, the reader, when reading rcnt > through rwsem_down_read_slowpath(), will see that rcnt is 0 and will > jump to the queue label. > > Thanks, > Tang Yes, so if rcnt > 1, the RWSEM_WRITER_LOCKED bit couldn't be set?