linux-kernel - [PATCH drm-misc-next v2 6/9] drm/fsl-dcu: plane: protect device resources after removal

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Date:   Sat,  1 Oct 2022 16:57:59 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     daniel@...ll.ch, airlied@...ux.ie, tzimmermann@...e.de,
        mripard@...nel.org, stefan@...er.ch, alison.wang@....com
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Danilo Krummrich <dakr@...hat.com>
Subject: [PATCH drm-misc-next v2 6/9] drm/fsl-dcu: plane: protect device resources after removal

(Hardware) resources which are bound to the driver and device lifecycle
must not be accessed after the device and driver are unbound.

However, the DRM device isn't freed as long as the last user didn't
close it, hence userspace can still call into the driver.

Therefore protect the critical sections which are accessing those
resources with drm_dev_enter() and drm_dev_exit().

Signed-off-by: Danilo Krummrich <dakr@...hat.com>
---
 drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c | 24 +++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c
index 23ff285da477..b1305f0af9d5 100644
--- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c
+++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c
@@ -10,6 +10,7 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_crtc.h>
+#include <drm/drm_drv.h>
 #include <drm/drm_fb_dma_helper.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>
@@ -65,15 +66,21 @@ static void fsl_dcu_drm_plane_atomic_disable(struct drm_plane *plane,
 {
 	struct fsl_dcu_drm_device *fsl_dev = drm_to_fsl_dcu_drm_dev(plane->dev);
 	unsigned int value;
-	int index;
+	int index, idx;
+
+	if (!drm_dev_enter(plane->dev, &idx))
+		return;
 
 	index = fsl_dcu_drm_plane_index(plane);
 	if (index < 0)
-		return;
+		goto out;
 
 	regmap_read(fsl_dev->regmap, DCU_CTRLDESCLN(index, 4), &value);
 	value &= ~DCU_LAYER_EN;
 	regmap_write(fsl_dev->regmap, DCU_CTRLDESCLN(index, 4), value);
+
+out:
+	drm_dev_exit(idx);
 }
 
 static void fsl_dcu_drm_plane_atomic_update(struct drm_plane *plane,
@@ -86,14 +93,17 @@ static void fsl_dcu_drm_plane_atomic_update(struct drm_plane *plane,
 	struct drm_framebuffer *fb = plane->state->fb;
 	struct drm_gem_dma_object *gem;
 	unsigned int alpha = DCU_LAYER_AB_NONE, bpp;
-	int index;
+	int index, idx;
 
-	if (!fb)
+	if (!drm_dev_enter(plane->dev, &idx))
 		return;
 
+	if (!fb)
+		goto out;
+
 	index = fsl_dcu_drm_plane_index(plane);
 	if (index < 0)
-		return;
+		goto out;
 
 	gem = drm_fb_dma_get_gem_obj(fb, 0);
 
@@ -126,7 +136,7 @@ static void fsl_dcu_drm_plane_atomic_update(struct drm_plane *plane,
 		bpp = FSL_DCU_YUV422;
 		break;
 	default:
-		return;
+		goto out;
 	}
 
 	regmap_write(fsl_dev->regmap, DCU_CTRLDESCLN(index, 1),
@@ -162,6 +172,8 @@ static void fsl_dcu_drm_plane_atomic_update(struct drm_plane *plane,
 			     DCU_LAYER_PRE_SKIP(0));
 	}
 
+out:
+	drm_dev_exit(idx);
 	return;
 }
 
-- 
2.37.3