drm: Undo damage to page_flip_ioctl

I screwed up rebasing of my patch in

commit 43968d7b806d7a7e021261294c583a216fddf0e5
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Sep 21 10:59:24 2016 +0200

    drm: Extract drm_plane.[hc]

which meant on error paths drm_crtc_vblank_put could be called without
a get, leading to an underrun of the refcount.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98020
Reported-and-tested-by: Andy Furniss <adf.lists@gmail.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161003082827.11586-1-daniel.vetter@ffwll.ch
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 39 insertions, 42 deletions

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 783aef8acab7..249c0ae52c6d 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -783,6 +783,45 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
         if (!crtc)
                 return -ENOENT;
 
+        if (crtc->funcs->page_flip_target) {
+                u32 current_vblank;
+                int r;
+
+                r = drm_crtc_vblank_get(crtc);
+                if (r)
+                        return r;
+
+                current_vblank = drm_crtc_vblank_count(crtc);
+
+                switch (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET) {
+                case DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE:
+                        if ((int)(target_vblank - current_vblank) > 1) {
+                                DRM_DEBUG("Invalid absolute flip target %u, "
+                                          "must be <= %u\n", target_vblank,
+                                          current_vblank + 1);
+                                drm_crtc_vblank_put(crtc);
+                                return -EINVAL;
+                        }
+                        break;
+                case DRM_MODE_PAGE_FLIP_TARGET_RELATIVE:
+                        if (target_vblank != 0 && target_vblank != 1) {
+                                DRM_DEBUG("Invalid relative flip target %u, "
+                                          "must be 0 or 1\n", target_vblank);
+                                drm_crtc_vblank_put(crtc);
+                                return -EINVAL;
+                        }
+                        target_vblank += current_vblank;
+                        break;
+                default:
+                        target_vblank = current_vblank +
+                                !(page_flip->flags & DRM_MODE_PAGE_FLIP_ASYNC);
+                        break;
+                }
+        } else if (crtc->funcs->page_flip == NULL ||
+                   (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET)) {
+                return -EINVAL;
+        }
+
         drm_modeset_lock_crtc(crtc, crtc->primary);
         if (crtc->primary->fb == NULL) {
                 /* The framebuffer is currently unbound, presumably
@@ -793,9 +832,6 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
                 goto out;
         }
 
-        if (crtc->funcs->page_flip == NULL)
-                goto out;
-
         fb = drm_framebuffer_lookup(dev, page_flip->fb_id);
         if (!fb) {
                 ret = -ENOENT;
@@ -839,45 +875,6 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
         }
 
         crtc->primary->old_fb = crtc->primary->fb;
-        if (crtc->funcs->page_flip_target) {
-                u32 current_vblank;
-                int r;
-
-                r = drm_crtc_vblank_get(crtc);
-                if (r)
-                        return r;
-
-                current_vblank = drm_crtc_vblank_count(crtc);
-
-                switch (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET) {
-                case DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE:
-                        if ((int)(target_vblank - current_vblank) > 1) {
-                                DRM_DEBUG("Invalid absolute flip target %u, "
-                                          "must be <= %u\n", target_vblank,
-                                          current_vblank + 1);
-                                drm_crtc_vblank_put(crtc);
-                                return -EINVAL;
-                        }
-                        break;
-                case DRM_MODE_PAGE_FLIP_TARGET_RELATIVE:
-                        if (target_vblank != 0 && target_vblank != 1) {
-                                DRM_DEBUG("Invalid relative flip target %u, "
-                                          "must be 0 or 1\n", target_vblank);
-                                drm_crtc_vblank_put(crtc);
-                                return -EINVAL;
-                        }
-                        target_vblank += current_vblank;
-                        break;
-                default:
-                        target_vblank = current_vblank +
-                                !(page_flip->flags & DRM_MODE_PAGE_FLIP_ASYNC);
-                        break;
-                }
-        } else if (crtc->funcs->page_flip == NULL ||
-                   (page_flip->flags & DRM_MODE_PAGE_FLIP_TARGET)) {
-                return -EINVAL;
-        }
-
         if (crtc->funcs->page_flip_target)
                 ret = crtc->funcs->page_flip_target(crtc, fb, e,
                                                     page_flip->flags,