drm/qxl: fix lockdep issue in qxl_alloc_release_reserved

Call qxl_bo_unpin (which does a reservation) without holding the
release_mutex lock.  Fixes lockdep (correctly) warning on a possible
deadlock.

Fixes: 65ffea3c ("drm/qxl: unpin release objects")
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20210217123213.2199186-5-kraxel@redhat.com

drivers/gpu/drm/qxl/qxl_release.c

@@ -283,7 +283,7 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
 				       int type, struct qxl_release **release,
 				       struct qxl_bo **rbo)
 {
-	struct qxl_bo *bo;
+	struct qxl_bo *bo, *free_bo = NULL;
 	int idr_ret;
 	int ret = 0;
 	union qxl_release_info *info;
@@ -315,8 +315,7 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
 
 	mutex_lock(&qdev->release_mutex);
 	if (qdev->current_release_bo_offset[cur_idx] + 1 >= releases_per_bo[cur_idx]) {
-		qxl_bo_unpin(qdev->current_release_bo[cur_idx]);
-		qxl_bo_unref(&qdev->current_release_bo[cur_idx]);
+		free_bo = qdev->current_release_bo[cur_idx];
 		qdev->current_release_bo_offset[cur_idx] = 0;
 		qdev->current_release_bo[cur_idx] = NULL;
 	}
@@ -324,6 +323,10 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
 		ret = qxl_release_bo_alloc(qdev, &qdev->current_release_bo[cur_idx], priority);
 		if (ret) {
 			mutex_unlock(&qdev->release_mutex);
+			if (free_bo) {
+				qxl_bo_unpin(free_bo);
+				qxl_bo_unref(&free_bo);
+			}
 			qxl_release_free(qdev, *release);
 			return ret;
 		}
@@ -339,6 +342,10 @@ int qxl_alloc_release_reserved(struct qxl_device *qdev, unsigned long size,
 		*rbo = bo;
 
 	mutex_unlock(&qdev->release_mutex);
+	if (free_bo) {
+		qxl_bo_unpin(free_bo);
+		qxl_bo_unref(&free_bo);
+	}
 
 	ret = qxl_release_list_add(*release, bo);
 	qxl_bo_unref(&bo);