drm: Don't assert held reservation lock for dma-buf mmapping

Don't assert held dma-buf reservation lock on memory mapping of exported
buffer.

We're going to change dma-buf mmap() locking policy such that exporters
will have to handle the lock. The previous locking policy caused deadlock
problem for DRM drivers in a case of self-imported dma-bufs once these
drivers are moved to use reservation lock universally. The problem is
solved by moving the lock down to exporters. This patch prepares DRM
drivers for the locking policy update.
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230529223935.2672495-2-dmitry.osipenko@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/20230529223935.2672495-3-dmitry.osipenko@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/20230529223935.2672495-4-dmitry.osipenko@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/20230529223935.2672495-2-dmitry.osipenko@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/20230529223935.2672495-3-dmitry.osipenko@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/20230529223935.2672495-4-dmitry.osipenko@collabora.com

drivers/gpu/drm/drm_prime.c

@@ -778,8 +778,6 @@ int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma)
 {
 	struct drm_gem_object *obj = dma_buf->priv;
 
-	dma_resv_assert_held(dma_buf->resv);
-
 	return drm_gem_prime_mmap(obj, vma);
 }
 EXPORT_SYMBOL(drm_gem_dmabuf_mmap);

drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c

@@ -97,8 +97,6 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	int ret;
 
-	dma_resv_assert_held(dma_buf->resv);
-
 	if (obj->base.size < vma->vm_end - vma->vm_start)
 		return -EINVAL;
 

drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c

@@ -66,8 +66,6 @@ static int omap_gem_dmabuf_mmap(struct dma_buf *buffer,
 	struct drm_gem_object *obj = buffer->priv;
 	int ret = 0;
 
-	dma_resv_assert_held(buffer->resv);
-
 	ret = drm_gem_mmap_obj(obj, omap_gem_mmap_size(obj), vma);
 	if (ret < 0)
 		return ret;

drivers/gpu/drm/tegra/gem.c

@@ -694,8 +694,6 @@ static int tegra_gem_prime_mmap(struct dma_buf *buf, struct vm_area_struct *vma)
 	struct drm_gem_object *gem = buf->priv;
 	int err;
 
-	dma_resv_assert_held(buf->resv);
-
 	err = drm_gem_mmap_obj(gem, gem->size, vma);
 	if (err < 0)
 		return err;