On 2025-01-31 11:58, Xiaogang.Chen wrote:
> From: Xiaogang Chen <xiaogang.chen@xxxxxxx>
>
> When register a vm range at svm the added vm range may be split into multiple
> subranges and/or existing pranges got spitted. The new pranges need validated
> and mapped. This patch changes error handling for pranges that fail updating:
It may help if you clearly state the problem you're trying to solve to justify the changes in error handling. See more comments inline.
>
> 1: free prange resources and remove it from svms if its updating fails as it
> will not be used.
> 2: return -EAGAIN when all pranges at update_list need redo valid/map,
> otherwise return no -EAGAIN error to user space to indicate failure. That
> removes unnecessary retries.
>
> Signed-off-by: Xiaogang Chen <xiaogang.chen@xxxxxxx>
> ---
> drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index e32e19196f6b..455cb98bf16a 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -3716,8 +3716,19 @@ svm_range_set_attr(struct kfd_process *p, struct mm_struct *mm,
>
> out_unlock_range:
> mutex_unlock(&prange->migrate_mutex);
> - if (r)
> - ret = r;
> + /* this prange cannot be migraed, valid or map */
> + if (r) {
> + /* free this prange resources, remove it from svms */
> + svm_range_unlink(prange);
> + svm_range_remove_notifier(prange);
> + svm_range_free(prange, false);
Freeing the prange removes SVM mappings from the process. This will break the subsequent execution of the application. In case you were going to return -EAGAIN that's definitely wrong because the application would expect the SVM range to work after a successful retry.
I'm not sure the resource waste is a valid argument in case of a fatal error. I would expect the application to terminate anyways in this case, which would result in freeing the resources. Do you see a scenario where an application wants to continue running after this function returned a fatal error?
> +
> + /* ret got update when any r != -EAGAIN;
> + * return -EAGAIN when all pranges at update_list
> + * need redo valid/map */
> + if (r != -EAGAIN || !ret)
> + ret = r;
This is a good point. But the explanation is a bit misleading: "all pranges ... need redo" is not really true. There may also be ranges that were validated successfully. I think the point you're trying to make is this: Don't return -EAGAIN if there was any previous fatal error found.
I could potentially see a different optimization. If you encounter a fatal error, you can skip the rest of the ranges and return the error immediately.
> + }
> }
>
> list_for_each_entry(prange, &remap_list, update_list) {
> @@ -3729,8 +3740,16 @@ svm_range_set_attr(struct kfd_process *p, struct mm_struct *mm,
> if (r)
> pr_debug("failed %d on remap svm range\n", r);
> mutex_unlock(&prange->migrate_mutex);
> - if (r)
> - ret = r;
> +
> + if (r) {
> + /* remove this prange */
> + svm_range_unlink(prange);
> + svm_range_remove_notifier(prange);
> + svm_range_free(prange, false);
Same as above.
Regards,
Felix
> +
> + if (r != -EAGAIN || !ret)
> + ret = r;
> + }
> }
>
> dynamic_svm_range_dump(svms);
