drm/tegra: Fix lockup on a use of staging API

Commit bdd2f9cd ("Don't leak kernel pointer to userspace") added a
mutex around staging IOCTL's, some of those mutexes are taken twice.

Fixes: bdd2f9cd ("drm/tegra: Don't leak kernel pointer to userspace")
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: http://patchwork.freedesktop.org/patch/msgid/7b70a506a9d2355ea6ff19a8c4f4d726b67719b3.1497480754.git.digetx@gmail.com

drivers/gpu/drm/tegra/drm.c

@@ -451,18 +451,6 @@ int tegra_drm_submit(struct tegra_drm_context *context,
 
 
 #ifdef CONFIG_DRM_TEGRA_STAGING
-static struct tegra_drm_context *
-tegra_drm_file_get_context(struct tegra_drm_file *file, u32 id)
-{
-	struct tegra_drm_context *context;
-
-	mutex_lock(&file->lock);
-	context = idr_find(&file->contexts, id);
-	mutex_unlock(&file->lock);
-
-	return context;
-}
-
 static int tegra_gem_create(struct drm_device *drm, void *data,
 			    struct drm_file *file)
 {
@@ -606,7 +594,7 @@ static int tegra_close_channel(struct drm_device *drm, void *data,
 
 	mutex_lock(&fpriv->lock);
 
-	context = tegra_drm_file_get_context(fpriv, args->context);
+	context = idr_find(&fpriv->contexts, args->context);
 	if (!context) {
 		err = -EINVAL;
 		goto unlock;
@@ -631,7 +619,7 @@ static int tegra_get_syncpt(struct drm_device *drm, void *data,
 
 	mutex_lock(&fpriv->lock);
 
-	context = tegra_drm_file_get_context(fpriv, args->context);
+	context = idr_find(&fpriv->contexts, args->context);
 	if (!context) {
 		err = -ENODEV;
 		goto unlock;
@@ -660,7 +648,7 @@ static int tegra_submit(struct drm_device *drm, void *data,
 
 	mutex_lock(&fpriv->lock);
 
-	context = tegra_drm_file_get_context(fpriv, args->context);
+	context = idr_find(&fpriv->contexts, args->context);
 	if (!context) {
 		err = -ENODEV;
 		goto unlock;
@@ -685,7 +673,7 @@ static int tegra_get_syncpt_base(struct drm_device *drm, void *data,
 
 	mutex_lock(&fpriv->lock);
 
-	context = tegra_drm_file_get_context(fpriv, args->context);
+	context = idr_find(&fpriv->contexts, args->context);
 	if (!context) {
 		err = -ENODEV;
 		goto unlock;