[PATCH 08/14] drm/amdkfd: Get reference to lead_thread task struct

[Oded Gabbay]

On Tue, Dec 5, 2017 at 9:14 PM, Felix Kuehling <felix.kuehling at amd.com> wrote:
> On 2017-12-05 03:43 AM, Oded Gabbay wrote:
>> On Tue, Nov 28, 2017 at 1:29 AM, Felix Kuehling <Felix.Kuehling at amd.com> wrote:
>>> Increment the kfd_process.lead_thread's reference counter to make
>>> it safe to dereference. This is needed for getting a safe reference
>>> to the process' mm_struct.
>> I don't object to this patch, but I thought we don't dereference the
>> process' mm_struct...
>
> Correct. Instead we get the mm by calling get_task_mm(p->lead_thread).
> But for that we need to properly hold a reference to the task. Otherwise
> p->lead_thread may be pointing to a task that doesn't exist any more. I
> missed that part when I first ported that change.
>
> Regards,
>   Felix
Yes, agreed (I missed that too).

This patch is:
Reviewed-by: Oded Gabbay <oded.gabbay at gmail.com>


>
>>
>> From kfd_priv.h:
>>
>> /*
>> * Opaque pointer to mm_struct. We don't hold a reference to
>> * it so it should never be dereferenced from here. This is
>> * only used for looking up processes by their mm.
>> */
>> void *mm;
>>
>>
>>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>>> ---
>>>  drivers/gpu/drm/amd/amdkfd/kfd_process.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> index 99c18ee..660d8bc 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> @@ -24,6 +24,7 @@
>>>  #include <linux/log2.h>
>>>  #include <linux/sched.h>
>>>  #include <linux/sched/mm.h>
>>> +#include <linux/sched/task.h>
>>>  #include <linux/slab.h>
>>>  #include <linux/amd-iommu.h>
>>>  #include <linux/notifier.h>
>>> @@ -191,6 +192,8 @@ static void kfd_process_wq_release(struct work_struct *work)
>>>
>>>         mutex_destroy(&p->mutex);
>>>
>>> +       put_task_struct(p->lead_thread);
>>> +
>>>         kfree(p);
>>>
>>>         kfree(work);
>>> @@ -342,6 +345,7 @@ static struct kfd_process *create_process(const struct task_struct *thread)
>>>                         (uintptr_t)process->mm);
>>>
>>>         process->lead_thread = thread->group_leader;
>>> +       get_task_struct(process->lead_thread);
>>>
>>>         INIT_LIST_HEAD(&process->per_device_data);
>>>
>>> --
>>> 2.7.4
>>>
>