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 <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>

drivers/gpu/drm/exynos/exynos_drm_drv.c

···
 #include <drm/drmP.h>
 #include <drm/drm_crtc_helper.h>
 
+#include <linux/anon_inodes.h>
+
 #include <drm/exynos_drm.h>
 
 #include "exynos_drm_drv.h"
···
 	return 0;
 }
 
+static const struct file_operations exynos_drm_gem_fops = {
+	.mmap = exynos_drm_gem_mmap_buffer,
+};
+
 static int exynos_drm_open(struct drm_device *dev, struct drm_file *file)
 {
 	struct drm_exynos_file_private *file_priv;
+	struct file *anon_filp;
 	int ret;
 
 	file_priv = kzalloc(sizeof(*file_priv), GFP_KERNEL);
···
 		file->driver_priv = NULL;
 	}
 
+	anon_filp = anon_inode_getfile("exynos_gem", &exynos_drm_gem_fops,
+					NULL, 0);
+	if (IS_ERR(anon_filp)) {
+		kfree(file_priv);
+		return PTR_ERR(anon_filp);
+	}
+
+	anon_filp->f_mode = FMODE_READ | FMODE_WRITE;
+	file_priv->anon_filp = anon_filp;
+
 	return ret;
 }
 
···
 static void exynos_drm_postclose(struct drm_device *dev, struct drm_file *file)
 {
 	struct exynos_drm_private *private = dev->dev_private;
+	struct drm_exynos_file_private *file_priv;
 	struct drm_pending_vblank_event *v, *vt;
 	struct drm_pending_event *e, *et;
 	unsigned long flags;
···
 	}
 	spin_unlock_irqrestore(&dev->event_lock, flags);
 
+	file_priv = file->driver_priv;
+	if (file_priv->anon_filp)
+		fput(file_priv->anon_filp);
 
 	kfree(file->driver_priv);
 	file->driver_priv = NULL;

drivers/gpu/drm/exynos/exynos_drm_drv.h

···
 struct drm_exynos_file_private {
 	struct exynos_drm_g2d_private	*g2d_priv;
 	struct exynos_drm_ipp_private	*ipp_priv;
+	struct file			*anon_filp;
 };
 
 /*

drivers/gpu/drm/exynos/exynos_drm_gem.c

···
 			&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);
 
···
 	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)) {
···
 		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);
+	exynos_file_priv = file_priv->driver_priv;
+	anon_filp = exynos_file_priv->anon_filp;
+	anon_filp->private_data = obj;
 
-	/*
-	 * 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;
-
-	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;
 	}

drivers/gpu/drm/exynos/exynos_drm_gem.h

···
 int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *file_priv);
 
+int exynos_drm_gem_mmap_buffer(struct file *filp,
+				      struct vm_area_struct *vma);
+
 /* map user space allocated by malloc to pages. */
 int exynos_drm_gem_userptr_ioctl(struct drm_device *dev, void *data,
 				      struct drm_file *file_priv);