drm/exynos: use a new anon file for exynos gem mmaper

This patch resolves potential deadlock issue that can be incurred
by changing file->f_op and filp->private_data to exynos specific
mapper ops and gem object temporarily.

To resolve this issue, this patch creates a new anon file dedicated
to exynos specific mmaper, and making it used instead of existing one.

Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

1 files changed, 13 insertions, 61 deletions

diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
index 1ade191d84f4..49b8c9b22902 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
@@ -338,46 +338,22 @@ int exynos_drm_gem_map_offset_ioctl(struct drm_device *dev, void *data,
 			&args->offset);
 }
 
-static struct drm_file *exynos_drm_find_drm_file(struct drm_device *drm_dev,
-							struct file *filp)
-{
-	struct drm_file *file_priv;
-
-	/* find current process's drm_file from filelist. */
-	list_for_each_entry(file_priv, &drm_dev->filelist, lhead)
-		if (file_priv->filp == filp)
-			return file_priv;
-
-	WARN_ON(1);
-
-	return ERR_PTR(-EFAULT);
-}
-
-static int exynos_drm_gem_mmap_buffer(struct file *filp,
+int exynos_drm_gem_mmap_buffer(struct file *filp,
 				      struct vm_area_struct *vma)
 {
 	struct drm_gem_object *obj = filp->private_data;
 	struct exynos_drm_gem_obj *exynos_gem_obj = to_exynos_gem_obj(obj);
 	struct drm_device *drm_dev = obj->dev;
 	struct exynos_drm_gem_buf *buffer;
-	struct drm_file *file_priv;
 	unsigned long vm_size;
 	int ret;
 
+	WARN_ON(!mutex_is_locked(&obj->dev->struct_mutex));
+
 	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_private_data = obj;
 	vma->vm_ops = drm_dev->driver->gem_vm_ops;
 
-	/* restore it to driver's fops. */
-	filp->f_op = fops_get(drm_dev->driver->fops);
-
-	file_priv = exynos_drm_find_drm_file(drm_dev, filp);
-	if (IS_ERR(file_priv))
-		return PTR_ERR(file_priv);
-
-	/* restore it to drm_file. */
-	filp->private_data = file_priv;
-
 	update_vm_cache_attr(exynos_gem_obj, vma);
 
 	vm_size = vma->vm_end - vma->vm_start;
@@ -411,15 +387,13 @@ static int exynos_drm_gem_mmap_buffer(struct file *filp,
 	return 0;
 }
 
-static const struct file_operations exynos_drm_gem_fops = {
-	.mmap = exynos_drm_gem_mmap_buffer,
-};
-
 int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *file_priv)
 {
+	struct drm_exynos_file_private *exynos_file_priv;
 	struct drm_exynos_gem_mmap *args = data;
 	struct drm_gem_object *obj;
+	struct file *anon_filp;
 	unsigned long addr;
 
 	if (!(dev->driver->driver_features & DRIVER_GEM)) {
@@ -427,47 +401,25 @@ int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
 		return -ENODEV;
 	}
 
+	mutex_lock(&dev->struct_mutex);
+
 	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
 	if (!obj) {
 		DRM_ERROR("failed to lookup gem object.\n");
+		mutex_unlock(&dev->struct_mutex);
 		return -EINVAL;
 	}
 
-	/*
-	 * We have to use gem object and its fops for specific mmaper,
-	 * but vm_mmap() can deliver only filp. So we have to change
-	 * filp->f_op and filp->private_data temporarily, then restore
-	 * again. So it is important to keep lock until restoration the
-	 * settings to prevent others from misuse of filp->f_op or
-	 * filp->private_data.
-	 */
-	mutex_lock(&dev->struct_mutex);
-
-	/*
-	 * Set specific mmper's fops. And it will be restored by
-	 * exynos_drm_gem_mmap_buffer to dev->driver->fops.
-	 * This is used to call specific mapper temporarily.
-	 */
-	file_priv->filp->f_op = &exynos_drm_gem_fops;
-
-	/*
-	 * Set gem object to private_data so that specific mmaper
-	 * can get the gem object. And it will be restored by
-	 * exynos_drm_gem_mmap_buffer to drm_file.
-	 */
-	file_priv->filp->private_data = obj;
+	exynos_file_priv = file_priv->driver_priv;
+	anon_filp = exynos_file_priv->anon_filp;
+	anon_filp->private_data = obj;
 
-	addr = vm_mmap(file_priv->filp, 0, args->size,
-			PROT_READ | PROT_WRITE, MAP_SHARED, 0);
+	addr = vm_mmap(anon_filp, 0, args->size, PROT_READ | PROT_WRITE,
+			MAP_SHARED, 0);
 
 	drm_gem_object_unreference(obj);
 
 	if (IS_ERR_VALUE(addr)) {
-		/* check filp->f_op, filp->private_data are restored */
-		if (file_priv->filp->f_op == &exynos_drm_gem_fops) {
-			file_priv->filp->f_op = fops_get(dev->driver->fops);
-			file_priv->filp->private_data = file_priv;
-		}
 		mutex_unlock(&dev->struct_mutex);
 		return (int)addr;
 	}