linux-kernel - [PATCH 2/2] drm/bridge: Add extra checks in pre_enable and post

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Date:   Fri, 25 Feb 2022 14:45:04 +0100
From:   Ricardo Cañuelo <ricardo.canuelo@...labora.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Ricardo Cañuelo <ricardo.canuelo@...labora.com>,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        kernel@...labora.com, andrzej.hajda@...el.com,
        narmstrong@...libre.com, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org
Subject: [PATCH 2/2] drm/bridge: Add extra checks in pre_enable and post_enable

Depending on the bridge code, certain userspace events during a driver
teardown (such as a DRM ioctl call) might cause a race condition where
the drm_bridge_chain_pre_enable() and drm_bridge_chain_post_enable()
functions could be called for a bridge that has just been detached and
removed from the bridge chain of an encoder.

This change makes these functions a bit more robust by bailing out if
the bridge has already been detached.

Tested on an Acer Chromebook R13 (Elm, MT8173) with Debian Sid.

Signed-off-by: Ricardo Cañuelo <ricardo.canuelo@...labora.com>
---
 drivers/gpu/drm/drm_bridge.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index c96847fc0ebc..e074aa456dd1 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -529,7 +529,7 @@ void drm_bridge_chain_post_disable(struct drm_bridge *bridge)
 {
 	struct drm_encoder *encoder;
 
-	if (!bridge)
+	if (!bridge || !bridge->dev)
 		return;
 
 	encoder = bridge->encoder;
@@ -585,7 +585,7 @@ void drm_bridge_chain_pre_enable(struct drm_bridge *bridge)
 	struct drm_encoder *encoder;
 	struct drm_bridge *iter;
 
-	if (!bridge)
+	if (!bridge || !bridge->dev)
 		return;
 
 	encoder = bridge->encoder;
-- 
2.25.1