From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prarit Bhargava Subject: Re: [PATCH 5/5] cpufreq, add BUG() messages in critical paths to aid debugging failures Date: Sat, 08 Nov 2014 08:33:35 -0500 Message-ID: <545E1BAF.4060801@redhat.com> References: <1415199239-19019-1-git-send-email-prarit@redhat.com> <1415199239-19019-6-git-send-email-prarit@redhat.com> <1908314.5SSPFg5MrY@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60463 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753650AbaKHNdv (ORCPT ); Sat, 8 Nov 2014 08:33:51 -0500 In-Reply-To: <1908314.5SSPFg5MrY@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: linux-kernel@vger.kernel.org, robert.schoene@tu-dresden.de, sboyd@codeaurora.org, Viresh Kumar , linux-pm@vger.kernel.org On 11/07/2014 09:00 PM, Rafael J. Wysocki wrote: > On Wednesday, November 05, 2014 09:53:59 AM Prarit Bhargava wrote: >> Add some additional debug to capture failures in the locking scheme for >> cpufreq. Instead of just a NULL pointer, these warnings will capture failure >> points if the locking scheme for cpufreq is broken. >> >> Cc: "Rafael J. Wysocki" >> Cc: Viresh Kumar >> Cc: linux-pm@vger.kernel.org >> Signed-off-by: Prarit Bhargava >> --- >> drivers/cpufreq/cpufreq_governor.c | 32 +++++++++++++++++++++++++++----- >> 1 file changed, 27 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c >> index b1ee597..f158882 100644 >> --- a/drivers/cpufreq/cpufreq_governor.c >> +++ b/drivers/cpufreq/cpufreq_governor.c >> @@ -161,9 +161,18 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu) >> EXPORT_SYMBOL_GPL(dbs_check_cpu); >> >> static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data, >> - unsigned int delay) >> + unsigned int delay, >> + struct cpufreq_policy *policy) >> { >> - struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu); >> + struct cpu_dbs_common_info *cdbs; >> + >> + if (!dbs_data->cdata) { >> + pr_emerg("common_dbs_data is NULL for %s but initialized = %d", >> + policy->governor->name, >> + atomic_read(&policy->governor->initialized)); >> + BUG(); > > Is it necessary to crash the kernel here? Yes. dbs_data->cdata is referenced right below. > >> + } >> + cdbs = dbs_data->cdata->get_cpu_cdbs(cpu); and we'll NULL pointer panic right here without any of the debug info above :( >> >> mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay); >> } >> @@ -185,10 +194,11 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy, >> * those works are canceled during CPU_DOWN_PREPARE so they >> * can't possibly run on any other CPU. >> */ >> - __gov_queue_work(raw_smp_processor_id(), dbs_data, delay); >> + __gov_queue_work(raw_smp_processor_id(), dbs_data, delay, >> + policy); >> } else { >> for_each_cpu(i, policy->cpus) >> - __gov_queue_work(i, dbs_data, delay); >> + __gov_queue_work(i, dbs_data, delay, policy); >> } >> >> out_unlock: >> @@ -258,7 +268,13 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy, >> else >> dbs_data = cdata->gdbs_data; >> >> - WARN_ON(!dbs_data && (event != CPUFREQ_GOV_POLICY_INIT)); >> + if (!dbs_data && (event != CPUFREQ_GOV_POLICY_INIT)) { >> + pr_emerg("governor_data is NULL but governor %s is initialized = %d [governor_enabled = %d event = %u]\n", >> + policy->governor->name, >> + atomic_read(&policy->governor->initialized), >> + policy->governor_enabled, event); >> + BUG(); > > And here? > Ditto -- dbs_data is dereferenced in the call path and will NULL pointer panic. P. >> + } >> >> switch (event) { >> case CPUFREQ_GOV_POLICY_INIT: >> @@ -329,6 +345,12 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy, >> case CPUFREQ_GOV_POLICY_EXIT: >> mutex_lock(&dbs_data->usage_count_mutex); >> if (atomic_dec_and_test(&dbs_data->usage_count)) { >> + if (atomic_read(&policy->governor->initialized) > 1) { >> + pr_emerg("Removing governor %s but initialized = %d, dbs_data->usage_count = 0\n", >> + policy->governor->name, >> + atomic_read(&policy->governor->initialized)); >> + BUG(); >> + } >> sysfs_remove_group(get_governor_parent_kobj(policy), >> get_sysfs_attr(dbs_data)); >> >> >