[PATCH v2] drm/gem: add mutex lock when using drm_gem_mmap_obj

[Rob Clark]

On Wed, Jun 26, 2013 at 7:39 PM, Seung-Woo Kim <sw0312.kim at samsung.com> wrote:
> From: YoungJun Cho <yj44.cho at samsung.com>
>
> The drm_gem_mmap_obj() has to be protected with dev->struct_mutex,
> but some caller functions do not. So it adds mutex lock to missing
> callers and adds assertion to check whether drm_gem_mmap_obj() is
> called with mutex lock or not.

Yeah, looks like since drm_gem_mmap_obj() is using
drm_vm_open_locked() (vs drm_vm_open() / vm_ops->open()), we need
this.  I missed that when reviewing the original patch to
drm_gem_mmap_obj()'ify things.

Reviewed-by: Rob Clark <robdclark at gmail.com>


> Signed-off-by: YoungJun Cho <yj44.cho at samsung.com>
> Signed-off-by: Seung-Woo Kim <sw0312.kim at samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
> CC: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
> CC: Rob Clark <robdclark at gmail.com>
> ---
> This patch is based on drm-next branch.
>
> Changes since v1:
> - Use lockdep_assert_held() instead of mutex_is_locked() as Maarten commented
> - Fix commit message about assertion
>
>  drivers/gpu/drm/drm_gem.c                 |    4 ++++
>  drivers/gpu/drm/drm_gem_cma_helper.c      |    3 +++
>  drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c |    3 +++
>  3 files changed, 10 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 4321713..34c0be7 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -661,6 +661,8 @@ EXPORT_SYMBOL(drm_gem_vm_close);
>   * the GEM object is not looked up based on its fake offset. To implement the
>   * DRM mmap operation, drivers should use the drm_gem_mmap() function.
>   *
> + * NOTE: This function has to be protected with dev->struct_mutex
> + *
>   * Return 0 or success or -EINVAL if the object size is smaller than the VMA
>   * size, or if no gem_vm_ops are provided.
>   */
> @@ -669,6 +671,8 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
>  {
>         struct drm_device *dev = obj->dev;
>
> +       lockdep_assert_held(&dev->struct_mutex);
> +
>         /* Check for valid size. */
>         if (obj_size < vma->vm_end - vma->vm_start)
>                 return -EINVAL;
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 9efabce..ce06397 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -487,9 +487,12 @@ static int drm_gem_cma_dmabuf_mmap(struct dma_buf *dmabuf,
>  {
>         struct drm_gem_cma_object *cma_obj = dmabuf->priv;
>         struct drm_gem_object *gem_obj = &cma_obj->base;
> +       struct drm_device *dev = gem_obj->dev;
>         int ret;
>
> +       mutex_lock(&dev->struct_mutex);
>         ret = drm_gem_mmap_obj(gem_obj, gem_obj->size, vma);
> +       mutex_unlock(&dev->struct_mutex);
>         if (ret < 0)
>                 return ret;
>
> diff --git a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> index 3256693..4fcca8d 100644
> --- a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> +++ b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> @@ -140,12 +140,15 @@ static int omap_gem_dmabuf_mmap(struct dma_buf *buffer,
>                 struct vm_area_struct *vma)
>  {
>         struct drm_gem_object *obj = buffer->priv;
> +       struct drm_device *dev = obj->dev;
>         int ret = 0;
>
>         if (WARN_ON(!obj->filp))
>                 return -EINVAL;
>
> +       mutex_lock(&dev->struct_mutex);
>         ret = drm_gem_mmap_obj(obj, omap_gem_mmap_size(obj), vma);
> +       mutex_unlock(&dev->struct_mutex);
>         if (ret < 0)
>                 return ret;
>
> --
> 1.7.9.5
>