1 files changed, 42 insertions, 6 deletions

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 80d556402ab4..c4c704e01961 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -51,6 +51,37 @@
 /* from BKL pushdown */
 DEFINE_MUTEX(drm_global_mutex);
 
+bool drm_dev_needs_global_mutex(struct drm_device *dev)
+{
+	/*
+	 * Legacy drivers rely on all kinds of BKL locking semantics, don't
+	 * bother. They also still need BKL locking for their ioctls, so better
+	 * safe than sorry.
+	 */
+	if (drm_core_check_feature(dev, DRIVER_LEGACY))
+		return true;
+
+	/*
+	 * The deprecated ->load callback must be called after the driver is
+	 * already registered. This means such drivers rely on the BKL to make
+	 * sure an open can't proceed until the driver is actually fully set up.
+	 * Similar hilarity holds for the unload callback.
+	 */
+	if (dev->driver->load || dev->driver->unload)
+		return true;
+
+	/*
+	 * Drivers with the lastclose callback assume that it's synchronized
+	 * against concurrent opens, which again needs the BKL. The proper fix
+	 * is to use the drm_client infrastructure with proper locking for each
+	 * client.
+	 */
+	if (dev->driver->lastclose)
+		return true;
+
+	return false;
+}
+
 /**
  * DOC: file operations
  *
@@ -378,9 +409,10 @@ int drm_open(struct inode *inode, struct file *filp)
 	if (IS_ERR(minor))
 		return PTR_ERR(minor);
 
-	mutex_lock(&drm_global_mutex);
-
 	dev = minor->dev;
+	if (drm_dev_needs_global_mutex(dev))
+		mutex_lock(&drm_global_mutex);
+
 	if (!atomic_fetch_inc(&dev->open_count))
 		need_setup = 1;
 
@@ -398,13 +430,15 @@ int drm_open(struct inode *inode, struct file *filp)
 		}
 	}
 
-	mutex_unlock(&drm_global_mutex);
+	if (drm_dev_needs_global_mutex(dev))
+		mutex_unlock(&drm_global_mutex);
 
 	return 0;
 
 err_undo:
 	atomic_dec(&dev->open_count);
-	mutex_unlock(&drm_global_mutex);
+	if (drm_dev_needs_global_mutex(dev))
+		mutex_unlock(&drm_global_mutex);
 	drm_minor_release(minor);
 	return retcode;
 }
@@ -444,7 +478,8 @@ int drm_release(struct inode *inode, struct file *filp)
 	struct drm_minor *minor = file_priv->minor;
 	struct drm_device *dev = minor->dev;
 
-	mutex_lock(&drm_global_mutex);
+	if (drm_dev_needs_global_mutex(dev))
+		mutex_lock(&drm_global_mutex);
 
 	DRM_DEBUG("open_count = %d\n", atomic_read(&dev->open_count));
 
@@ -453,7 +488,8 @@ int drm_release(struct inode *inode, struct file *filp)
 	if (atomic_dec_and_test(&dev->open_count))
 		drm_lastclose(dev);
 
-	mutex_unlock(&drm_global_mutex);
+	if (drm_dev_needs_global_mutex(dev))
+		mutex_unlock(&drm_global_mutex);
 
 	drm_minor_release(minor);