[PATCH] drm/amdkfd: change kfd process kref count at creation

[Felix Kuehling]

On 2024-10-09 14:08, Xiaogang.Chen wrote:
> From: Xiaogang Chen <xiaogang.chen at amd.com>
>
> kfd process kref count(process->ref) is initialized to 1 by kref_init. After
> it is created not need to increaes its kref. Instad add kfd process kref at kfd
> process mmu notifier allocation since we decrease the ref at free_notifier of
> mmu_notifier_ops, so pair them.

That's not correct. kfd_create_process returns a struct kfd_process * 
reference. That gets stored by the caller in filep->private_data. That 
requires incrementing the reference count. You can have multiple 
references to the same struct kfd_process if user mode opens /dev/kfd 
multiple times. The reference is released in kfd_release. Your change 
breaks that use case.

The reference released in kfd_process_free_notifier is only one per 
process and it's the reference created by kref_init.

Regards,
   Felix


>
> Signed-off-by: Xiaogang Chen <Xiaogang.Chen at amd.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_process.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> index d07acf1b2f93..7c5471d7d743 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> @@ -899,8 +899,6 @@ struct kfd_process *kfd_create_process(struct task_struct *thread)
>   		init_waitqueue_head(&process->wait_irq_drain);
>   	}
>   out:
> -	if (!IS_ERR(process))
> -		kref_get(&process->ref);
>   	mutex_unlock(&kfd_processes_mutex);
>   	mmput(thread->mm);
>   
> @@ -1191,7 +1189,11 @@ static struct mmu_notifier *kfd_process_alloc_notifier(struct mm_struct *mm)
>   
>   	srcu_read_unlock(&kfd_processes_srcu, idx);
>   
> -	return p ? &p->mmu_notifier : ERR_PTR(-ESRCH);
> +	if (p) {
> +		kref_get(&p->ref);
> +		return &p->mmu_notifier;
> +	}
> +	return ERR_PTR(-ESRCH);
>   }
>   
>   static void kfd_process_free_notifier(struct mmu_notifier *mn)