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 590A5C43334 for ; Tue, 14 Jun 2022 13:59:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242070AbiFNN7S (ORCPT ); Tue, 14 Jun 2022 09:59:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245328AbiFNN7N (ORCPT ); Tue, 14 Jun 2022 09:59:13 -0400 Received: from mail-yw1-f175.google.com (mail-yw1-f175.google.com [209.85.128.175]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADD683334C; Tue, 14 Jun 2022 06:59:12 -0700 (PDT) Received: by mail-yw1-f175.google.com with SMTP id 00721157ae682-30ce6492a60so30351447b3.8; Tue, 14 Jun 2022 06:59:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=DiRdL8duDyIHD6Nrt/s9DO6S9xYvs+pewZXGWKr83oU=; b=F7+lDjB1LY8+C+uCiKKFDC/cJqlxZAcGXl7nB/Q5PoIFZOgo9quo68RClHJmF2F5/O vtifMor1FWSdVJNUQ1m3+8O3M3TKDk9+VqDosQYUFqsDykdMwwB3ZmNEJjBpdQAS533w 0esdkmVWCl0t0JlUP6gNxnCpJOKlRFWbNVCwgZ4owuhOxmlp+3EtSgi7pjJ/cvDCU7qD 3Hr8ziTpXLn7d10RjU7YJr5lvVIQatu1y2N+1NN+a66EuXd8wjxDYv/2pPw74ONBLEE0 DrtPJ+v93x7zkg3gYkAsyCQhnC3ayWy8zyBqmThlkh5iazDVnQsAmfWFBJb1MGtWv8h9 /7wQ== X-Gm-Message-State: AJIora/qv8vYmiV6nkCsDJK51EfEpDBlBUKnkuh+77c1YYOOGKI0XnqN /umtXsQNjRq0ywMeK+co39EqBdTNqtZKpTYSKAygV8q0/0w= X-Google-Smtp-Source: AGRyM1sFQuBs2xBokqAiNhHO7MCfL0HvIR4LcShp/DTuYO2FaLXtI5Mr+Cz8F2WU2HiJkgoLukiKankCmyFZUXoLeYA= X-Received: by 2002:a81:260a:0:b0:2f4:ca82:a42f with SMTP id m10-20020a81260a000000b002f4ca82a42fmr5931264ywm.149.1655215151897; Tue, 14 Jun 2022 06:59:11 -0700 (PDT) MIME-Version: 1.0 References: <8c3d50faf8811e86136fb3f9c459e43fc3c50bc0.1653565641.git.viresh.kumar@linaro.org> <426bf6edc80b2e944d459fa7b8dffbe8b73bb3d9.1653623526.git.viresh.kumar@linaro.org> In-Reply-To: <426bf6edc80b2e944d459fa7b8dffbe8b73bb3d9.1653623526.git.viresh.kumar@linaro.org> From: "Rafael J. Wysocki" Date: Tue, 14 Jun 2022 15:59:01 +0200 Message-ID: Subject: Re: [PATCH V2 2/3] cpufreq: Panic if policy is active in cpufreq_policy_free() To: Viresh Kumar Cc: "Rafael J. Wysocki" , Linux PM , Vincent Guittot , kernel test robot , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Fri, May 27, 2022 at 5:53 AM Viresh Kumar wrote: > > With the new design in place, to avoid potential races show() and > store() callbacks check if the policy is active or not before proceeding > any further. And in order to guarantee that cpufreq_policy_free() must > be called after clearing the policy->cpus mask, i.e. by marking it > inactive. > > Lets make sure we don't get a bug around this later and catch this early > by putting a BUG_ON() within cpufreq_policy_free(). > > Also update cpufreq_online() a bit to make sure we clear the cpus mask > for each error case before calling cpufreq_policy_free(). > > Signed-off-by: Viresh Kumar > --- > V2: Update cpufreq_online() and changelog. > > drivers/cpufreq/cpufreq.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index e24aa5d4bca5..0f8245731783 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1284,6 +1284,12 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy) > unsigned long flags; > int cpu; > > + /* > + * The callers must ensure the policy is inactive by now, to avoid any > + * races with show()/store() callbacks. > + */ > + BUG_ON(!policy_is_inactive(policy)); I'm not a super-big fan of this change. First off, crashing the kernel outright here because of possible races appears a bit excessive to me. Second, it looks like we are worrying about the code running before the wait_for_completion() call in cpufreq_policy_put_kobj(), because after that call no one can be running show() or store(). So why don't we reorder the wait_for_completion() call with respect to the code in question instead? > + > /* Remove policy from list */ > write_lock_irqsave(&cpufreq_driver_lock, flags); > list_del(&policy->policy_list); > @@ -1538,8 +1544,6 @@ static int cpufreq_online(unsigned int cpu) > for_each_cpu(j, policy->real_cpus) > remove_cpu_dev_symlink(policy, j, get_cpu_device(j)); > > - cpumask_clear(policy->cpus); > - > out_offline_policy: > if (cpufreq_driver->offline) > cpufreq_driver->offline(policy); > @@ -1549,6 +1553,7 @@ static int cpufreq_online(unsigned int cpu) > cpufreq_driver->exit(policy); > > out_free_policy: > + cpumask_clear(policy->cpus); > up_write(&policy->rwsem); > > cpufreq_policy_free(policy); > -- > 2.31.1.272.g89b43f80a514 >