From patchwork Sat Aug 26 09:58:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liao Chang X-Patchwork-Id: 717360 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 6863AC83F13 for ; Sat, 26 Aug 2023 10:01:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232164AbjHZKBH (ORCPT ); Sat, 26 Aug 2023 06:01:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231280AbjHZKAi (ORCPT ); Sat, 26 Aug 2023 06:00:38 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5C1DE5; Sat, 26 Aug 2023 03:00:35 -0700 (PDT) Received: from kwepemd100002.china.huawei.com (unknown [172.30.72.54]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4RXsgS4nnHzJrsx; Sat, 26 Aug 2023 17:57:24 +0800 (CST) Received: from huawei.com (10.67.174.28) by kwepemd100002.china.huawei.com (7.221.188.184) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.1258.23; Sat, 26 Aug 2023 18:00:32 +0800 From: Liao Chang To: , , CC: , Subject: [PATCH] cpufreq: Fix the race condition while updating the transition_task of policy Date: Sat, 26 Aug 2023 09:58:36 +0000 Message-ID: <20230826095836.1138608-1-liaochang1@huawei.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Originating-IP: [10.67.174.28] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemd100002.china.huawei.com (7.221.188.184) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org The field 'transition_task' of policy structure is used to track the task which is performing the frequency transition. Using this field to print a warning once detect a case where the same task is calling _begin() again before completing the preivous frequency transition via the _end(). However, there is a potential race condition in _end() and _begin() APIs while updating the field 'transition_task' of policy, the scenario is depicted below: Task A Task B /* 1st freq transition */ Invoke _begin() { ... ... } /* 2nd freq transition */ Invoke _begin() { ... //waiting for A to ... //clear ... //transition_ongoing ... //in _end() for ... //the 1st transition | Change the frequency | | Invoke _end() { | ... | ... | transition_ongoing = false; V transition_ongoing = true; transition_task = current; transition_task = NULL; ... //A overwrites the task ... //performing the transition ... //result in error warning. } To fix this race condition, the order of the updates to the 'transition_task' and 'transition_ongoing' fields has been changed, the 'transition_task' field is now cleared before the 'transition_ongoing' field, which ensure that only one task can update the 'transition_task' field at a time. Fixes: ca654dc3a93d ("cpufreq: Catch double invocations of cpufreq_freq_transition_begin/end") Signed-off-by: Liao Chang --- drivers/cpufreq/cpufreq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index a757f90aa9d6..f8eb6dde57f2 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -455,8 +455,8 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy, policy->cur, policy->cpuinfo.max_freq); - policy->transition_ongoing = false; policy->transition_task = NULL; + policy->transition_ongoing = false; wake_up(&policy->transition_wait); }