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 23C71C4332F for ; Fri, 21 Oct 2022 06:11:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230096AbiJUGLl convert rfc822-to-8bit (ORCPT ); Fri, 21 Oct 2022 02:11:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49664 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230086AbiJUGLj (ORCPT ); Fri, 21 Oct 2022 02:11:39 -0400 Received: from out30-44.freemail.mail.aliyun.com (out30-44.freemail.mail.aliyun.com [115.124.30.44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A6E36109D64; Thu, 20 Oct 2022 23:11:37 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R771e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046059;MF=guanjun@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0VSi31.b_1666332694; Received: from smtpclient.apple(mailfrom:guanjun@linux.alibaba.com fp:SMTPD_---0VSi31.b_1666332694) by smtp.aliyun-inc.com; Fri, 21 Oct 2022 14:11:35 +0800 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 15.0 \(3693.40.0.1.81\)) Subject: Re: [PATCH 1/1] cpufreq: Fix show()/store() issue for hotplugging offline CPU From: guanjun In-Reply-To: Date: Fri, 21 Oct 2022 14:11:33 +0800 Cc: schspa@gmail.com, viresh.kumar@linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, "zelin.deng@linux.alibaba.com" Content-Transfer-Encoding: 8BIT Message-Id: <149754EC-1CD5-4D6C-90C6-6F13AB319C00@linux.alibaba.com> References: <1666168845-67690-1-git-send-email-guanjun@linux.alibaba.com> <1666168845-67690-2-git-send-email-guanjun@linux.alibaba.com> To: "Rafael J. Wysocki" X-Mailer: Apple Mail (2.3693.40.0.1.81) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rafael, > 2022年10月19日 下午7:47，Rafael J. Wysocki 写道： > > On Wed, Oct 19, 2022 at 10:40 AM Guanjun wrote: >> >> From: Zelin Deng >> >> After brought one CPU offline, lscpu returned failure: >> >> lscpu: cannot read /sys/devices/system/cpu/cpu64/cpufreq/cpuinfo_max_freq: Device or resource busy >> >> which had blocked all outputs of lscpu. > > OK, so the policy->cpus mask is empty and -EBUSY is returned. > > What's wrong? Here is all right. The problem is that when I offline one cpu manually and lscpu will fail. The reproduce process is as follows: 1. lscpu （success） 2. echo 0 > /sys/devices/system/cpu/cpu63/online （offline cpu63） 3. lscpu （fail， and print the error message, “lscpu: cannot read /sys/devices/system/cpu/cpu64/cpufreq/cpuinfo_max_freq: Device or resource busy”） I think this failure doesn’t make sense. Maybe I should make the commit message more readable. Thanks, Guanjun > >> This is not the case mentioned in commit d4627a287e251, as the policy >> had been created successfully but is inactive due to CPU gets offline. > > Yes, that's when policy_is_inactive(policy) returns "true" IIUC. > >> To fix this issue, just add an addtional check whether CPU is online or >> not. > > Which is racy. > > Please explain the problem in the first place. > >> Fixes: d4627a287e251 ("cpufreq: Abort show()/store() for half-initialized policies") >> Signed-off-by: Zelin Deng >> Signed-off-by: Guanjun >> --- >> drivers/cpufreq/cpufreq.c | 16 ++++++++++++---- >> 1 file changed, 12 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >> index 69b3d61852ac..aa238ba7d2fe 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c >> @@ -956,8 +956,12 @@ static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf) >> return -EIO; >> >> down_read(&policy->rwsem); >> - if (likely(!policy_is_inactive(policy))) >> - ret = fattr->show(policy, buf); >> + if (unlikely(policy_is_inactive(policy) && cpu_online(policy->cpu))) >> + goto err; >> + >> + ret = fattr->show(policy, buf); >> + >> +err: >> up_read(&policy->rwsem); >> >> return ret; >> @@ -974,8 +978,12 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr, >> return -EIO; >> >> down_write(&policy->rwsem); >> - if (likely(!policy_is_inactive(policy))) >> - ret = fattr->store(policy, buf, count); >> + if (unlikely(policy_is_inactive(policy) && cpu_online(policy->cpu))) >> + goto err; >> + >> + ret = fattr->store(policy, buf, count); >> + >> +err: >> up_write(&policy->rwsem); >> >> return ret; >> -- >> 2.32.0.GIT