release/5.2.30/drm-damage_helper-Fix-race-checking-plane-state-fb.patch

From 180dc5b1fa97d066bbb4494352de3214b57d79d5 Mon Sep 17 00:00:00 2001
From: Sean Paul <seanpaul@chromium.org>
Date: Wed, 4 Sep 2019 16:29:13 -0400
Subject: [PATCH] drm: damage_helper: Fix race checking plane->state->fb

commit 354c2d310082d1c384213ba76c3757dd3cd8755d upstream.

Since the dirtyfb ioctl doesn't give us any hints as to which plane is
scanning out the fb it's marking as damaged, we need to loop through
planes to find it.

Currently we just reach into plane state and check, but that can race
with another commit changing the fb out from under us. This patch locks
the plane before checking the fb and will release the lock if the plane
is not displaying the dirty fb.

Fixes: b9fc5e01d1ce ("drm: Add helper to implement legacy dirtyfb")
Cc: Rob Clark <robdclark@gmail.com>
Cc: Deepak Rawat <drawat@vmware.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.0+
Reported-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190904202938.110207-1-sean@poorly.run
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c
index ee67c96841fa..f7219474bda1 100644
--- a/drivers/gpu/drm/drm_damage_helper.c
+++ b/drivers/gpu/drm/drm_damage_helper.c
@@ -212,8 +212,14 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
 	drm_for_each_plane(plane, fb->dev) {
 		struct drm_plane_state *plane_state;
 
-		if (plane->state->fb != fb)
+		ret = drm_modeset_lock(&plane->mutex, state->acquire_ctx);
+		if (ret)
+			goto out;
+
+		if (plane->state->fb != fb) {
+			drm_modeset_unlock(&plane->mutex);
 			continue;
+		}
 
 		plane_state = drm_atomic_get_plane_state(state, plane);
 		if (IS_ERR(plane_state)) {
-- 
2.7.4