[PATCH] drm/amdkfd: fix some race conditions in vram buffer alloc/free of svm code

[Felix Kuehling]

On 2023-09-20 2:17, Xiaogang.Chen wrote:
> From: Xiaogang Chen <xiaogang.chen at amd.com>
>
> This patch fixes:
> 1: ref number of prange's svm_bo got decreased by an async call from hmm. When
> wait svm_bo of prange got released we shoul also wait prang->svm_bo become NULL,
> otherwise prange->svm_bo may be set to null after allocate new vram buffer.

I agree with this part.


>
> 2: During waiting svm_bo of prange got released in a while loop should schedule
> current task to give other tasks oppotunity to run, specially the the workque
> task that handles svm_bo ref release, otherwise we may enter to softlock.

We had a similar discussion a few weeks back for another soft lock and I 
pointed to  cond_reschedule, which seems to be the preferred way to 
avoid soft locks in the kernel. Does cond_reschedule work for this case?

Regards,
   Felix


>
> Signed-off-by: Xiaogang.Chen <Xiaogang.Chen at amd.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index bed0f8bf83c7..1074a4aedf57 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -502,11 +502,11 @@ svm_range_validate_svm_bo(struct kfd_node *node, struct svm_range *prange)
>   
>   	/* We need a new svm_bo. Spin-loop to wait for concurrent
>   	 * svm_range_bo_release to finish removing this range from
> -	 * its range list. After this, it is safe to reuse the
> -	 * svm_bo pointer and svm_bo_list head.
> +	 * its range list and set prange->svm_bo to null. After this,
> +	 * it is safe to reuse the svm_bo pointer and svm_bo_list head.
>   	 */
> -	while (!list_empty_careful(&prange->svm_bo_list))
> -		;
> +	while (!list_empty_careful(&prange->svm_bo_list) || prange->svm_bo)
> +		schedule();
>   
>   	return false;
>   }