From: jsg <jsg@openbsd.org>
Date: Mon, 9 Sep 2024 08:18:38 +0000 (+0000)
Subject: drm/fb-helper: Don't schedule_work() to flush frame buffer during panic()
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=61e353b93e080559c59c1e11498bd378adf8bb5e;p=openbsd

drm/fb-helper: Don't schedule_work() to flush frame buffer during panic()

From Qiuxu Zhuo
d5618eaea8868e2534c375b8a512693658068cf8 in linux-6.6.y/6.6.50
833cd3e9ad8360785b6c23c82dd3856df00732d9 in mainline linux
---

diff --git a/sys/dev/pci/drm/drm_fb_helper.c b/sys/dev/pci/drm/drm_fb_helper.c
index 1a0be9cb24e..18a9d1def98 100644
--- a/sys/dev/pci/drm/drm_fb_helper.c
+++ b/sys/dev/pci/drm/drm_fb_helper.c
@@ -647,6 +647,17 @@ static void drm_fb_helper_add_damage_clip(struct drm_fb_helper *helper, u32 x, u
 static void drm_fb_helper_damage(struct drm_fb_helper *helper, u32 x, u32 y,
 				 u32 width, u32 height)
 {
+	/*
+	 * This function may be invoked by panic() to flush the frame
+	 * buffer, where all CPUs except the panic CPU are stopped.
+	 * During the following schedule_work(), the panic CPU needs
+	 * the worker_pool lock, which might be held by a stopped CPU,
+	 * causing schedule_work() and panic() to block. Return early on
+	 * oops_in_progress to prevent this blocking.
+	 */
+	if (oops_in_progress)
+		return;
+
 	drm_fb_helper_add_damage_clip(helper, x, y, width, height);
 
 	schedule_work(&helper->damage_work);