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=-1.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS 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 4DA20ECE562 for ; Wed, 19 Sep 2018 05:19:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 040D320877 for ; Wed, 19 Sep 2018 05:19:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="LcIx5cmZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 040D320877 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730880AbeISKzR (ORCPT ); Wed, 19 Sep 2018 06:55:17 -0400 Received: from aserp2120.oracle.com ([141.146.126.78]:34494 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726827AbeISKzQ (ORCPT ); Wed, 19 Sep 2018 06:55:16 -0400 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w8J5IuNK137264; Wed, 19 Sep 2018 05:19:01 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=2NyCwPocYTtt1gHksHJfAJKwThQnTDY3VpexHxiclKk=; b=LcIx5cmZC69gZ9WpXyDErJzZ7Z1GilFJLJGiqHkzskAwC3DbFS13BFWbqUV7k9vv7xLm oFk5sFe36ecMniSVc7UI0SriudIL1UhWIVAZB+U45vOZn9BWhyS1c7fPbLMOoBJIpZWj cQgUsazgFsCh+hEWtwXlRWjtvUaBtUeKUPdU/6N5K7xw3/qRqFmSm7pgC/Huzie1HiDB iR8L7ndo1+fayvIHArucn5682hM/6m84pfDtZKfkBtG8MskAtmR+QQU3qkpAZDB2YjyE 0/tQN/IWfPze4n4SrEHR42TCBmMcd3OnAmQu39JY+5Y3tWqhv44BcFwZdpXn/p3V1InQ yA== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by aserp2120.oracle.com with ESMTP id 2mgt1prnf8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 19 Sep 2018 05:19:01 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w8J5J0Ja005856 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 19 Sep 2018 05:19:00 GMT Received: from abhmp0001.oracle.com (abhmp0001.oracle.com [141.146.116.7]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w8J5J0J3025782; Wed, 19 Sep 2018 05:19:00 GMT Received: from [10.182.70.180] (/10.182.70.180) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 18 Sep 2018 22:18:59 -0700 Subject: Re: [PATCH 2/4] lib/percpu-refcount: introduce percpu_ref_resurge() To: Ming Lei , linux-kernel@vger.kernel.org Cc: Tejun Heo , Kent Overstreet , linux-block@vger.kernel.org References: <20180918101946.13329-1-ming.lei@redhat.com> <20180918101946.13329-3-ming.lei@redhat.com> From: "jianchao.wang" Message-ID: <242969d0-1370-b342-025d-a11b7f59d28f@oracle.com> Date: Wed, 19 Sep 2018 13:19:10 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180918101946.13329-3-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9020 signatures=668707 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=661 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1809190055 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ming On 09/18/2018 06:19 PM, Ming Lei wrote: > + unsigned long __percpu *percpu_count; > + > + WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count)); > + > + /* get one extra ref for avoiding race with .release */ > + rcu_read_lock_sched(); > + atomic_long_add(1, &ref->count); > + rcu_read_unlock_sched(); > + } The rcu_read_lock_sched here is redundant. We have been in the critical section of a spin_lock_irqsave. The atomic_long_add(1, &ref->count) may have two result. 1. ref->count > 1 it will not drop to zero any more. 2. ref->count == 1 it has dropped to zero and .release may be running. Thanks Jianchao