Re: [PATCH] drm/amdkfd: Fix a race condition of vram buffer unref in svm code

[Eric Huang <jinhuieric.huang@amd.com>]

On 2023-09-26 23:00, Xiaogang.Chen wrote:
> From: Xiaogang Chen <xiaogang.chen@amd.com>
>
> prange->svm_bo unref can happen in both mmu callback and a callback after
> migrate to system ram. Both are async call in different tasks. Sync svm_bo
> unref operation to avoid random "use-after-free".
>
> Signed-off-by: Xiaogang.Chen <Xiaogang.Chen@amd.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index 70aa882636ab..8e246e848018 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -637,6 +637,15 @@ void svm_range_vram_node_free(struct svm_range *prange)
>   {
>   	svm_range_bo_unref(prange->svm_bo);
>   	prange->ttm_res = NULL;
Are above two lines not removed?

Regards,
Eric
> +	/* serialize prange->svm_bo unref */
> +	mutex_lock(&prange->lock);
> +	/* prange->svm_bo has not been unref */
> +	if (prange->ttm_res) {
> +		prange->ttm_res = NULL;
> +		mutex_unlock(&prange->lock);
> +		svm_range_bo_unref(prange->svm_bo);
> +	} else
> +		mutex_unlock(&prange->lock);
>   }
>   
>   struct kfd_node *