[PATCH] drm/fb-helper: Fix drm_fb_helper_hotplug_event() NULL ptr argument

[Noralf Trønnes]

drm_fb_helper_hotplug_event() should tolerate the fb_helper argument being
NULL. Commit 03a9606e7fee ("drm/fb-helper: Avoid race with DRM userspace")
introduced a fb_helper dereference before the NULL check.
Fixup by moving the dereference after the NULL check.

Fixes: 03a9606e7fee ("drm/fb-helper: Avoid race with DRM userspace")
Reported-by: kbuild test robot <lkp at intel.com>
Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
---
 drivers/gpu/drm/drm_fb_helper.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index c259a28522f8..a52b48fafbd7 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -3031,7 +3031,6 @@ EXPORT_SYMBOL(drm_fb_helper_initial_config);
  */
 int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 {
-	struct drm_device *dev = fb_helper->dev;
 	int err = 0;
 
 	if (!drm_fbdev_emulation || !fb_helper)
@@ -3044,13 +3043,13 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
 		return err;
 	}
 
-	if (!fb_helper->fb || !drm_master_internal_acquire(dev)) {
+	if (!fb_helper->fb || !drm_master_internal_acquire(fb_helper->dev)) {
 		fb_helper->delayed_hotplug = true;
 		mutex_unlock(&fb_helper->lock);
 		return err;
 	}
 
-	drm_master_internal_release(dev);
+	drm_master_internal_release(fb_helper->dev);
 
 	DRM_DEBUG_KMS("\n");
 
-- 
2.20.1