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 CB9E4C433EF for ; Wed, 6 Jul 2022 13:49:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233621AbiGFNt2 (ORCPT ); Wed, 6 Jul 2022 09:49:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233552AbiGFNtY (ORCPT ); Wed, 6 Jul 2022 09:49:24 -0400 Received: from mail-yw1-f177.google.com (mail-yw1-f177.google.com [209.85.128.177]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 861541E3DC; Wed, 6 Jul 2022 06:49:21 -0700 (PDT) Received: by mail-yw1-f177.google.com with SMTP id 00721157ae682-31c9b70c382so78127607b3.6; Wed, 06 Jul 2022 06:49:21 -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=dtlZocyToFGVGM2MQv4D5WyH03DgmYnmulWgb2UYDDM=; b=5sTNTd959nviLdhYXPo32JN94yMddzVGvOEmZR2Gbt6cIsyfUPytCQC9x1WCuSGKXy xLGuAEkDEmsR45ND6N65PRlQRjdb3iNrjCHNFNJaZewKUkJxpde2JFeBH9Ds6HilX+GF EWggPWcj6SBJHSmoqT8GRItcG6X+gciLi5JoGLf3GM4tDqbsKmxstvK3VPynj4fi7hxL disixYF6FyjiiO17AFwwFbu6AvkcRFX1iPj2Fa9VbGiytkzSixYzGdZ/4bA32IPazoh5 ITRVEkns6rbKjzvh7zCWs3bbmmp4bPHd7bNPLla153an+WqG+LKK/1AaVmM4J4EZc5I4 uVDw== X-Gm-Message-State: AJIora8/mjxVLZu67D2qghMyEjcjv7rP1GQOnE7WWOdIuIBQTpYWiBTE ypDTtzWSX3hYElUJ6Y0DBk9tiKb8jr7OGP1SXlA= X-Google-Smtp-Source: AGRyM1vr1wi9w9NCemLoidvbCweBYnR1fD94J+vYgMW//deWJxOLNs20DDiRmD9h3ILhGY+rqoURrgi4/Rat+LO9y+c= X-Received: by 2002:a81:17d0:0:b0:31c:c5e2:fc1e with SMTP id 199-20020a8117d0000000b0031cc5e2fc1emr10086071ywx.196.1657115360660; Wed, 06 Jul 2022 06:49:20 -0700 (PDT) MIME-Version: 1.0 References: <8c3d50faf8811e86136fb3f9c459e43fc3c50bc0.1653565641.git.viresh.kumar@linaro.org> <426bf6edc80b2e944d459fa7b8dffbe8b73bb3d9.1653623526.git.viresh.kumar@linaro.org> <20220615045957.55ocdyddcac3vwct@vireshk-i7> In-Reply-To: <20220615045957.55ocdyddcac3vwct@vireshk-i7> From: "Rafael J. Wysocki" Date: Wed, 6 Jul 2022 15:49:09 +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 Wed, Jun 15, 2022 at 7:00 AM Viresh Kumar wrote: > > On 14-06-22, 15:59, Rafael J. Wysocki wrote: > > 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? > > No, I am not worrying about that race. I am just trying to make sure some change > in future doesn't break this assumption (that policy should be inactive by this > point). That's all. It all looks good for now. > > May be a WARN instead of BUG if we don't want to crash. WARN_ON() would be somewhat better, but then I'm not sure if having a full call trace in this case is really useful, because we know when cpufreq_policy_free() can be called anyway. Maybe just print a warning message.