linux-kernel - [PATCH drm-misc-next v3 6/7] drm/arm/hdlcd: debugfs: protect device resources after removal

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Message-Id: <20221001011905.433408-7-dakr@redhat.com>
Date:   Sat,  1 Oct 2022 03:19:04 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     daniel@...ll.ch, airlied@...ux.ie, tzimmermann@...e.de,
        mripard@...nel.org, liviu.dudau@....com, brian.starkey@....com
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Danilo Krummrich <dakr@...hat.com>
Subject: [PATCH drm-misc-next v3 6/7] drm/arm/hdlcd: debugfs: 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/arm/hdlcd_drv.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/arm/hdlcd_drv.c b/drivers/gpu/drm/arm/hdlcd_drv.c
index e41def6d47cc..020c7d0c70a5 100644
--- a/drivers/gpu/drm/arm/hdlcd_drv.c
+++ b/drivers/gpu/drm/arm/hdlcd_drv.c
@@ -204,11 +204,19 @@ static int hdlcd_show_pxlclock(struct seq_file *m, void *arg)
 	struct drm_info_node *node = (struct drm_info_node *)m->private;
 	struct drm_device *drm = node->minor->dev;
 	struct hdlcd_drm_private *hdlcd = drm_to_hdlcd_priv(drm);
-	unsigned long clkrate = clk_get_rate(hdlcd->clk);
-	unsigned long mode_clock = hdlcd->crtc.mode.crtc_clock * 1000;
+	unsigned long clkrate, mode_clock;
+	int idx;
+
+	if (!drm_dev_enter(drm, &idx))
+		return -ENODEV;
+
+	clkrate = clk_get_rate(hdlcd->clk);
+	mode_clock = hdlcd->crtc.mode.crtc_clock * 1000;
 
 	seq_printf(m, "hw  : %lu\n", clkrate);
 	seq_printf(m, "mode: %lu\n", mode_clock);
+
+	drm_dev_exit(idx);
 	return 0;
 }
 
-- 
2.37.3