On Saturday, November 08, 2014 08:33:35 AM Prarit Bhargava wrote:
>
> 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" <r...@rjwysocki.net>
> >> Cc: Viresh Kumar <viresh.ku...@linaro.org>
> >> Cc: linux...@vger.kernel.org
> >> Signed-off-by: Prarit Bhargava <pra...@redhat.com>
> >> ---
> >> 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 :(
Can we possibly avoid the panic?
Adding BUG() instead of a NULL pointer deref is not much improvement.
>
> >>
> >> 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));
> >>
> >>
> >
> --
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--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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