drm/cirrus: Use drm_framebuffer_put to avoid kernel oops in clean-up

In the Cirrus driver, the regular clean-up code also performs the clean-up
of a failed initialization. If the fbdev's framebuffer was not initialized,
the clean-up will fail within drm_framebuffer_unregister_private. Booting
with cirrus.bpp=16 triggers this bug.

The framebuffer is currently stored directly within struct cirrus_fbdev. To
fix the bug, we turn it into a pointer that is only set for initialized
framebuffers. The fbdev's clean-up code skips uninitialized framebuffers.

The memory for struct drm_framebuffer is allocated dynamically. This requires
additional error handling within cirrusfb_create. The framebuffer clean-up is
now performed by drm_framebuffer_put, which also frees the data strcuture's
memory.

Link: https://bugzilla.suse.com/show_bug.cgi?id=1101822
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20180720112743.27159-1-tzimmermann@suse.de
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/cirrus/cirrus_drv.h

@@ -146,7 +146,7 @@ struct cirrus_device {
 
 struct cirrus_fbdev {
 	struct drm_fb_helper helper;
-	struct drm_framebuffer gfb;
+	struct drm_framebuffer *gfb;
 	void *sysram;
 	int size;
 	int x1, y1, x2, y2; /* dirty rect */

drivers/gpu/drm/cirrus/cirrus_fbdev.c

@@ -22,14 +22,14 @@ static void cirrus_dirty_update(struct cirrus_fbdev *afbdev,
 	struct drm_gem_object *obj;
 	struct cirrus_bo *bo;
 	int src_offset, dst_offset;
-	int bpp = afbdev->gfb.format->cpp[0];
+	int bpp = afbdev->gfb->format->cpp[0];
 	int ret = -EBUSY;
 	bool unmap = false;
 	bool store_for_later = false;
 	int x2, y2;
 	unsigned long flags;
 
-	obj = afbdev->gfb.obj[0];
+	obj = afbdev->gfb->obj[0];
 	bo = gem_to_cirrus_bo(obj);
 
 	/*
@@ -82,7 +82,7 @@ static void cirrus_dirty_update(struct cirrus_fbdev *afbdev,
 	}
 	for (i = y; i < y + height; i++) {
 		/* assume equal stride for now */
-		src_offset = dst_offset = i * afbdev->gfb.pitches[0] + (x * bpp);
+		src_offset = dst_offset = i * afbdev->gfb->pitches[0] + (x * bpp);
 		memcpy_toio(bo->kmap.virtual + src_offset, afbdev->sysram + src_offset, width * bpp);
 
 	}
@@ -192,23 +192,26 @@ static int cirrusfb_create(struct drm_fb_helper *helper,
 		return -ENOMEM;
 
 	info = drm_fb_helper_alloc_fbi(helper);
-	if (IS_ERR(info))
-		return PTR_ERR(info);
+	if (IS_ERR(info)) {
+		ret = PTR_ERR(info);
+		goto err_vfree;
+	}
 
 	info->par = gfbdev;
 
-	ret = cirrus_framebuffer_init(cdev->dev, &gfbdev->gfb, &mode_cmd, gobj);
+	fb = kzalloc(sizeof(*fb), GFP_KERNEL);
+	if (!fb) {
+		ret = -ENOMEM;
+		goto err_drm_gem_object_put_unlocked;
+	}
+
+	ret = cirrus_framebuffer_init(cdev->dev, fb, &mode_cmd, gobj);
 	if (ret)
-		return ret;
+		goto err_kfree;
 
 	gfbdev->sysram = sysram;
 	gfbdev->size = size;
-
-	fb = &gfbdev->gfb;
-	if (!fb) {
-		DRM_INFO("fb is NULL\n");
-		return -EINVAL;
-	}
+	gfbdev->gfb = fb;
 
 	/* setup helper */
 	gfbdev->helper.fb = fb;
@@ -241,24 +244,27 @@ static int cirrusfb_create(struct drm_fb_helper *helper,
 	DRM_INFO("   pitch is %d\n", fb->pitches[0]);
 
 	return 0;
+
+err_kfree:
+	kfree(fb);
+err_drm_gem_object_put_unlocked:
+	drm_gem_object_put_unlocked(gobj);
+err_vfree:
+	vfree(sysram);
+	return ret;
 }
 
 static int cirrus_fbdev_destroy(struct drm_device *dev,
 				struct cirrus_fbdev *gfbdev)
 {
-	struct drm_framebuffer *gfb = &gfbdev->gfb;
+	struct drm_framebuffer *gfb = gfbdev->gfb;
 
 	drm_fb_helper_unregister_fbi(&gfbdev->helper);
 
-	if (gfb->obj[0]) {
-		drm_gem_object_put_unlocked(gfb->obj[0]);
-		gfb->obj[0] = NULL;
-	}
-
 	vfree(gfbdev->sysram);
 	drm_fb_helper_fini(&gfbdev->helper);
-	drm_framebuffer_unregister_private(gfb);
-	drm_framebuffer_cleanup(gfb);
+	if (gfb)
+		drm_framebuffer_put(gfb);
 
 	return 0;
 }

drivers/gpu/drm/cirrus/cirrus_mode.c

@@ -127,7 +127,7 @@ static int cirrus_crtc_do_set_base(struct drm_crtc *crtc,
 		return ret;
 	}
 
-	if (&cdev->mode_info.gfbdev->gfb == crtc->primary->fb) {
+	if (cdev->mode_info.gfbdev->gfb == crtc->primary->fb) {
 		/* if pushing console in kmap it */
 		ret = ttm_bo_kmap(&bo->bo, 0, bo->bo.num_pages, &bo->kmap);
 		if (ret)