On 11/08/2014 04:46 PM, Rafael J. Wysocki wrote:
> 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" <[email protected]>
>>>> Cc: Viresh Kumar <[email protected]>
>>>> Cc: [email protected]
>>>> Signed-off-by: Prarit Bhargava <[email protected]>
>>>> ---
>>>> 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.
(sorry for the lowercase typing. i fractured my elbow and have resorted to
single hand typing ....)
rafael, i understand your concern and my description is clearly lacking for this
patch. this patch is not meant to be a fix but is meant to capture debug info
for future issues in this code. i thought about only doing the pr_emerg() but
that results in situations where other threads may continue processing and i
lose state in crashdump :(. bug() is a good idea here imo.
P.
>
>>
>>>>
>>>> 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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