Re: [PATCH 6/8] drm/panfrost: Make sure imported/exported BOs are never purged

[Steven Price <steven.price@arm.com>]

On 29/11/2019 13:59, Boris Brezillon wrote:
> We don't want imported/exported BOs to be purges, as those are shared

s/purges/purged/

> with other processes that might still use them. We should also refuse
> to export a BO if it's been marked purgeable or has already been purged.
> 
> Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_drv.c | 19 ++++++++++++++++-
>  drivers/gpu/drm/panfrost/panfrost_gem.c | 27 +++++++++++++++++++++++++
>  2 files changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 1c67ac434e10..751df975534f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -343,6 +343,7 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
>  	struct drm_panfrost_madvise *args = data;
>  	struct panfrost_device *pfdev = dev->dev_private;
>  	struct drm_gem_object *gem_obj;
> +	int ret;
>  
>  	gem_obj = drm_gem_object_lookup(file_priv, args->handle);
>  	if (!gem_obj) {
> @@ -350,6 +351,19 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
>  		return -ENOENT;
>  	}
>  
> +	/*
> +	 * We don't want to mark exported/imported BOs as purgeable: we're not
> +	 * the only owner in that case.
> +	 */
> +	mutex_lock(&dev->object_name_lock);
> +	if (gem_obj->dma_buf)
> +		ret = -EINVAL;
> +	else
> +		ret = 0;
> +
> +	if (ret)
> +		goto out_unlock_object_name;
> +

This might be better by setting ret = 0 at the beginning of the
function. This can then be re-written as the more normal:

	if (gem_obj->dma_buf) {
		ret = -EINVAL;
		goto out_unlock_object_name;
	]

>  	mutex_lock(&pfdev->shrinker_lock);
>  	args->retained = drm_gem_shmem_madvise(gem_obj, args->madv);
>  
> @@ -364,8 +378,11 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
>  	}
>  	mutex_unlock(&pfdev->shrinker_lock);
>  
> +out_unlock_object_name:
> +	mutex_unlock(&dev->object_name_lock);
> +
>  	drm_gem_object_put_unlocked(gem_obj);
> -	return 0;
> +	return ret;
>  }
>  
>  int panfrost_unstable_ioctl_check(void)
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 92a95210a899..31d6417dd21c 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -99,6 +99,32 @@ void panfrost_gem_close(struct drm_gem_object *obj, struct drm_file *file_priv)
>  	spin_unlock(&priv->mm_lock);
>  }
>  
> +static struct dma_buf *
> +panfrost_gem_export(struct drm_gem_object *obj, int flags)
> +{
> +	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> +	int ret;
> +
> +	/*
> +	 * We must make sure the BO has not been marked purgeable/purged before
> +	 * adding the mapping.
> +	 * Note that we don't need to protect this test with a lock because
> +	 * &drm_gem_object_funcs.export() is called with
> +	 * &drm_device.object_lock held, and panfrost_ioctl_madvise() takes
> +	 * this lock before calling drm_gem_shmem_madvise() (the function that
> +	 * modifies bo->base.madv).
> +	 */
> +	if (bo->base.madv == PANFROST_MADV_WILLNEED)
> +		ret = -EINVAL;
> +	else
> +		ret = 0;
> +
> +	if (ret)
> +		return ERR_PTR(ret);

No need for ret here:

	if (bo->base.madv == PANFROST_MADV_WILLNEED)
		return ERR_PTR(-EINVAL);

Steve

> +
> +	return drm_gem_prime_export(obj, flags);
> +}
> +
>  static int panfrost_gem_pin(struct drm_gem_object *obj)
>  {
>  	if (to_panfrost_bo(obj)->is_heap)
> @@ -112,6 +138,7 @@ static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>  	.open = panfrost_gem_open,
>  	.close = panfrost_gem_close,
>  	.print_info = drm_gem_shmem_print_info,
> +	.export = panfrost_gem_export,
>  	.pin = panfrost_gem_pin,
>  	.unpin = drm_gem_shmem_unpin,
>  	.get_sg_table = drm_gem_shmem_get_sg_table,
>