linux-kernel - [PATCH] drm/msm: Set drvdata to NULL when msm_drm

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Message-Id: <20210325212822.3663144-1-swboyd@chromium.org>
Date:   Thu, 25 Mar 2021 14:28:22 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Fabio Estevam <festevam@...il.com>,
        Krishna Manikandan <mkrishn@...eaurora.org>
Subject: [PATCH] drm/msm: Set drvdata to NULL when msm_drm_init() fails

We should set the platform device's driver data to NULL here so that
code doesn't assume the struct drm_device pointer is valid when it could
have been destroyed. The lifetime of this pointer is managed by a kref
but when msm_drm_init() fails we call drm_dev_put() on the pointer which
will free the pointer's memory. This driver uses the component model, so
there's sort of two "probes" in this file, one for the platform device
i.e. msm_pdev_probe() and one for the component i.e. msm_drm_bind(). The
msm_drm_bind() code is using the platform device's driver data to store
struct drm_device so the two functions are intertwined.

This relationship becomes a problem for msm_pdev_shutdown() when it
tests the NULL-ness of the pointer to see if it should call
drm_atomic_helper_shutdown(). The NULL test is a proxy check for if the
pointer has been freed by kref_put(). If the drm_device has been
destroyed, then we shouldn't call the shutdown helper, and we know that
is the case if msm_drm_init() failed, therefore set the driver data to
NULL so that this pointer liveness is tracked properly.

Fixes: 9d5cbf5fe46e ("drm/msm: add shutdown support for display platform_driver")
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Fabio Estevam <festevam@...il.com>
Cc: Krishna Manikandan <mkrishn@...eaurora.org>
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 drivers/gpu/drm/msm/msm_drv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index a5c6b8c23336..196907689c82 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -570,6 +570,7 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)
 	kfree(priv);
 err_put_drm_dev:
 	drm_dev_put(ddev);
+	platform_set_drvdata(pdev, NULL);
 	return ret;
 }

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