[Intel-gfx] [PATCH 6/8] drm/i915/gt: Fix memory leaks in per-gt sysfs

[Andrzej Hajda]

Hi Tvrtko,

On 10.05.2022 09:28, Tvrtko Ursulin wrote:
>
> On 29/04/2022 20:56, Ashutosh Dixit wrote:
>> All kmalloc'd kobjects need a kobject_put() to free memory. For 
>> example in
>> previous code, kobj_gt_release() never gets called. The requirement of
>> kobject_put() now results in a slightly different code organization.
>>
>> v2: s/gtn/gt/ (Andi)
>>
>> Cc: Andi Shyti <andi.shyti at intel.com>
>> Cc: Andrzej Hajda <andrzej.hajda at intel.com>
>> Fixes: b770bcfae9ad ("drm/i915/gt: create per-tile sysfs interface")
>> Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_gt.c       |  1 +
>>   drivers/gpu/drm/i915/gt/intel_gt_sysfs.c | 29 ++++++++++--------------
>>   drivers/gpu/drm/i915/gt/intel_gt_sysfs.h |  6 +----
>>   drivers/gpu/drm/i915/gt/intel_gt_types.h |  3 +++
>>   drivers/gpu/drm/i915/i915_sysfs.c        |  2 ++
>>   5 files changed, 19 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c 
>> b/drivers/gpu/drm/i915/gt/intel_gt.c
>> index 92394f13b42f..9aede288eb86 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_gt.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c
>> @@ -785,6 +785,7 @@ void intel_gt_driver_unregister(struct intel_gt *gt)
>>   {
>>       intel_wakeref_t wakeref;
>>   +    intel_gt_sysfs_unregister(gt);
>>       intel_rps_driver_unregister(&gt->rps);
>>       intel_gsc_fini(&gt->gsc);
>>   diff --git a/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c 
>> b/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c
>> index 8ec8bc660c8c..9e4ebf53379b 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c
>> @@ -24,7 +24,7 @@ bool is_object_gt(struct kobject *kobj)
>>     static struct intel_gt *kobj_to_gt(struct kobject *kobj)
>>   {
>> -    return container_of(kobj, struct kobj_gt, base)->gt;
>> +    return container_of(kobj, struct intel_gt, sysfs_gt);
>>   }
>>     struct intel_gt *intel_gt_sysfs_get_drvdata(struct device *dev,
>> @@ -72,9 +72,9 @@ static struct attribute *id_attrs[] = {
>>   };
>>   ATTRIBUTE_GROUPS(id);
>>   +/* A kobject needs a release() method even if it does nothing */
>>   static void kobj_gt_release(struct kobject *kobj)
>>   {
>> -    kfree(kobj);
>>   }
>>     static struct kobj_type kobj_gt_type = {
>> @@ -85,8 +85,6 @@ static struct kobj_type kobj_gt_type = {
>>     void intel_gt_sysfs_register(struct intel_gt *gt)
>>   {
>> -    struct kobj_gt *kg;
>> -
>>       /*
>>        * We need to make things right with the
>>        * ABI compatibility. The files were originally
>> @@ -98,25 +96,22 @@ void intel_gt_sysfs_register(struct intel_gt *gt)
>>       if (gt_is_root(gt))
>>           intel_gt_sysfs_pm_init(gt, gt_get_parent_obj(gt));
>>   -    kg = kzalloc(sizeof(*kg), GFP_KERNEL);
>> -    if (!kg)
>> +    /* init and xfer ownership to sysfs tree */
>> +    if (kobject_init_and_add(&gt->sysfs_gt, &kobj_gt_type,
>> +                 gt->i915->sysfs_gt, "gt%d", gt->info.id))
>
> Was there closure/agreement on the matter of whether or not there is a 
> potential race between "kfree(gt)" and sysfs access (last put from 
> sysfs that is)? I've noticed Andrzej and Ashutosh were discussing it 
> but did not read all the details.
>

Not really :)
IMO docs are against this practice, Ashutosh shows examples of this 
practice in code and according to his analysis it is safe.
I gave up looking for contradictions :) Either it is OK, kobject is not 
fully shared object, docs are obsolete and needs update, either the 
patch is wrong.
Anyway finally I tend to accept this solution, I failed to prove it is 
wrong :)
Acked-by: Andrzej Hajda <andrzej.hajda at intel.com>

Regards
Andrzej

Regards
Andrzej