drm/fb-helper: Fix a locking bug in an error path

The name of the function __drm_fb_helper_initial_config_and_unlock() and
also the comment above that function make it clear that all code paths
in this function should unlock fb_helper->lock before returning. Add a
mutex_unlock() call in the only code path where it is missing. This has
been detected by the Clang thread-safety analyzer.

Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Christian König <christian.koenig@amd.com> # radeon
Cc: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> # msm
Cc: Javier Martinez Canillas <javierm@redhat.com>
Fixes: 63c971a ("drm/fb-helper: Allocate and release fb_info in single place")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260403205355.1181984-1-bvanassche@acm.org

Author: bvanassche

drivers/gpu/drm/drm_fb_helper.c

@@ -1626,8 +1626,10 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper)
 	drm_client_modeset_probe(&fb_helper->client, width, height);
 
 	info = drm_fb_helper_alloc_info(fb_helper);
-	if (IS_ERR(info))
+	if (IS_ERR(info)) {
+		mutex_unlock(&fb_helper->lock);
 		return PTR_ERR(info);
+	}
 
 	ret = drm_fb_helper_single_fb_probe(fb_helper);
 	if (ret < 0) {