[PATCH 10/10] drm/vkms: No need for ->pages_lock in crc work anymore

[Rodrigo Siqueira]

On Thu, Jun 6, 2019 at 7:28 PM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> We're now guaranteed to no longer race against prepare_fb/cleanup_fb,
> which means we can access ->vaddr without having to hold a lock.
>
> Before the previous patches it was fairly easy to observe the cursor
> ->vaddr being invalid, but that's now gone, so we can upgrade to a
> full WARN_ON.
>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>
> Cc: Haneen Mohammed <hamohammed.sa at gmail.com>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> ---
>  drivers/gpu/drm/vkms/vkms_crc.c | 13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> index 0d31cfc32042..4b3146d83265 100644
> --- a/drivers/gpu/drm/vkms/vkms_crc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> @@ -97,16 +97,10 @@ static void compose_cursor(struct vkms_crc_data *cursor_crc,
>         cursor_obj = drm_gem_fb_get_obj(&cursor_crc->fb, 0);
>         cursor_vkms_obj = drm_gem_to_vkms_gem(cursor_obj);
>
> -       mutex_lock(&cursor_vkms_obj->pages_lock);
> -       if (!cursor_vkms_obj->vaddr) {
> -               DRM_WARN("cursor plane vaddr is NULL");
> -               goto out;
> -       }
> +       if (WARN_ON(!cursor_vkms_obj->vaddr))
> +               return;
>
>         blend(vaddr_out, cursor_vkms_obj->vaddr, primary_crc, cursor_crc);
> -
> -out:
> -       mutex_unlock(&cursor_vkms_obj->pages_lock);
>  }
>
>  static uint32_t _vkms_get_crc(struct vkms_crc_data *primary_crc,
> @@ -123,15 +117,12 @@ static uint32_t _vkms_get_crc(struct vkms_crc_data *primary_crc,
>                 return 0;
>         }
>
> -       mutex_lock(&vkms_obj->pages_lock);
>         if (WARN_ON(!vkms_obj->vaddr)) {
> -               mutex_unlock(&vkms_obj->pages_lock);
>                 kfree(vaddr_out);
>                 return crc;
>         }
>
>         memcpy(vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
> -       mutex_unlock(&vkms_obj->pages_lock);
>
>         if (cursor_crc)
>                 compose_cursor(cursor_crc, primary_crc, vaddr_out);
> --
> 2.20.1
>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>

-- 

Rodrigo Siqueira
https://siqueira.tech