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

[Felix Kuehling]

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

>
> 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
>>