Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751501AbbGIXi4 (ORCPT ); Thu, 9 Jul 2015 19:38:56 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:61270 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750744AbbGIXit (ORCPT ); Thu, 9 Jul 2015 19:38:49 -0400 From: "Rafael J. Wysocki" To: Viresh Kumar Cc: linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org, Pi-Cheng Chen , "Jon Medhurst (Tixy)" , open list , Steven Rostedt Subject: Re: [PATCH] cpufreq: Initialize the governor again while restoring policy Date: Fri, 10 Jul 2015 02:05:18 +0200 Message-ID: <5369372.r4v2a9W8l1@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20150709051024.GJ1805@linux> References: <3814282.YWYCHNROVv@vostro.rjw.lan> <20150709051024.GJ1805@linux> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3387 Lines: 82 On Thursday, July 09, 2015 10:40:24 AM Viresh Kumar wrote: > On 09-07-15, 02:33, Rafael J. Wysocki wrote: > > > We also missed marking policy->governor as NULL while restoring the > > > policy. Because of that, we call __cpufreq_governor(CPUFREQ_GOV_LIMITS) > > > > How exactly does that happen? > > Should have mentioned that in detail, sorry for being lazy. Hopefully > this will look better: OK, applied (with some minor changelog fixup), thanks! > ---------------------------8<--------------------------- > > Message-Id: <5f17361741c009a7f0d8488f7f94bab80d9317fd.1436418101.git.viresh.kumar@linaro.org> > From: Viresh Kumar > Date: Wed, 8 Jul 2015 10:45:53 +0530 > Subject: [PATCH V2] cpufreq: Initialize the governor again while restoring policy > > When all CPUs of a policy are hot-unplugged, we EXIT the governor but > don't mark policy->governor as NULL. This was done in order to keep last > used governor's information intact in sysfs, while the CPUs are offline. > > But we also marking policy->governor as NULL while restoring the policy. > > Because policy->governor still points to the last governor while policy > is restored, following sequence of event happens: > - cpufreq_init_policy() called while restoring policy > - find_governor() matches last_governor string for present governors and > returns last used governor's pointer, say ondemand. policy->governor > already has the same address, unless the governor was removed in > between. > - cpufreq_set_policy() is called with both old/new policies governor set > as ondemand. > - Because governors matched, we skip governor initialization and return > after calling __cpufreq_governor(CPUFREQ_GOV_LIMITS). But this sounds fragile in principle. What's the benefit from skipping the governor initialization in that case? > Because the > governor wasn't initialized for this policy, it returned -EBUSY. > - cpufreq_init_policy() exits the policy on this error, but doesn't > destroy it properly (should be fixed separately). > - And so we enter a scenario where the policy isn't completely > initialized but used. > > Fix this by setting policy->governor to NULL while restoring the policy. > > Reported-and-tested-by: Pi-Cheng Chen > Reported-and-tested-by: "Jon Medhurst (Tixy)" > Tested-by: Steven Rostedt > Fixes: 18bf3a124ef8 ("cpufreq: Mark policy->governor = NULL for inactive policies") > Signed-off-by: Viresh Kumar > --- > V2: Detailed changelog > > drivers/cpufreq/cpufreq.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index b612411655f9..2c22e3902e72 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1132,6 +1132,7 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu) > > down_write(&policy->rwsem); > policy->cpu = cpu; > + policy->governor = NULL; > up_write(&policy->rwsem); > } -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/