[Intel-xe] [PATCH 2/2] drm/xe: Properly remove the vma from the vm::notifer::rebind_list when destroyed

[Matthew Brost]

On Wed, May 10, 2023 at 04:19:32PM +0200, Thomas Hellström wrote:
> If a vma was destroyed with the bo evicted, it might happen that we forget
> to remove it from the notifer::rebind_list. Fix to make sure that really
> happens.
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_vm.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 5f93d78c2e58..f54b3b7566c9 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -978,6 +978,15 @@ static void xe_vma_destroy(struct xe_vma *vma, struct dma_fence *fence)
>  	} else {
>  		xe_bo_assert_held(vma->bo);
>  		list_del(&vma->bo_link);
> +		/*
> +		 * TODO: We can do an advisory check for list link empty here,
> +		 * if this lock becomes too costly. Nobody can re-add to the
> +		 * bo to the vm::notifier::rebind_list at this point since we
> +		 * have the bo lock.
> +		 */

IMO grab isn't a big deal, not sure this is worth such a lengthly comment.

> +		 spin_lock(&vm->notifier.list_lock);
> +		 list_del(&vma->notifier.rebind_link);

Can you safe call list_del on an empty list? I thought that call blows
up hence we have a bunch of if (!list_empty()) checks before calling
list_del all over the driver.

Matt

> +		 spin_unlock(&vm->notifier.list_lock);
>  		if (!vma->bo->vm)
>  			vm_remove_extobj(vma);
>  	}
> -- 
> 2.39.2
>