Re: [PATCH] drm/msm: Make .remove and .shutdown HW shutdown consistent

[Dmitry Baryshkov]

On Sun, 24 Jul 2022 at 00:09, Javier Martinez Canillas
<javierm@xxxxxxxxxx> wrote:
>
> Drivers' .remove and .shutdown callbacks are executed on different code
> paths. The former is called when a device is removed from the bus, while
> the latter is called at system shutdown time to quiesce the device.
>
> This means that some overlap exists between the two, because both have to
> take care of properly shutting down the hardware. But currently the logic
> used in these two callbacks isn't consistent in msm drivers, which could
> lead to kernel oops.
>
> For example, on .remove the component is deleted and its .unbind callback
> leads to the hardware being shutdown but only if the DRM device has been
> marked as registered.
>
> That check doesn't exist in the .shutdown logic and this can lead to the
> driver calling drm_atomic_helper_shutdown() for a DRM device that hasn't
> been properly initialized.
>
> A situation when this can happen is when a driver for an expected device
> fails to probe, since the .bind callback will never be executed.
>
> This bug was attempted to be fixed in commit 623f279c7781 ("drm/msm: fix
> shutdown hook in case GPU components failed to bind"), but unfortunately
> it still happens in some cases.
>
> Rather than trying to keep fixing in both places, let's unify in a single
> helper function that could be used for the two callbacks.
>
> Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
> ---
>
>  drivers/gpu/drm/msm/msm_drv.c | 31 +++++++++++++++++--------------
>  1 file changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 1ed4cd09dbf8..669891bd6f09 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -190,14 +190,8 @@ static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
>         return 0;
>  }
>
> -static int msm_drm_uninit(struct device *dev)
> +static void msm_shutdown_hw(struct drm_device *dev)
>  {
> -       struct platform_device *pdev = to_platform_device(dev);
> -       struct msm_drm_private *priv = platform_get_drvdata(pdev);
> -       struct drm_device *ddev = priv->dev;
> -       struct msm_kms *kms = priv->kms;
> -       int i;
> -
>         /*
>          * Shutdown the hw if we're far enough along where things might be on.
>          * If we run this too early, we'll end up panicking in any variety of
> @@ -205,10 +199,21 @@ static int msm_drm_uninit(struct device *dev)
>          * msm_drm_init, drm_dev->registered is used as an indicator that the
>          * shutdown will be successful.
>          */
> -       if (ddev->registered) {
> +       if (dev->registered)
> +               drm_atomic_helper_shutdown(dev);
> +}
> +
> +static int msm_drm_uninit(struct device *dev)
> +{
> +       struct platform_device *pdev = to_platform_device(dev);
> +       struct msm_drm_private *priv = platform_get_drvdata(pdev);
> +       struct drm_device *ddev = priv->dev;
> +       struct msm_kms *kms = priv->kms;
> +       int i;
> +
> +       if (ddev->registered)
>                 drm_dev_unregister(ddev);

No. The drm_dev_unregister() should come before drm_atomic_helper_shutdown().

Also drm_dev_unregister() should not be a part of .shutdown callback.
See the documentation in the drm_drv.c

> -               drm_atomic_helper_shutdown(ddev);
> -       }
> +       msm_shutdown_hw(ddev);
>
>         /* We must cancel and cleanup any pending vblank enable/disable
>          * work before msm_irq_uninstall() to avoid work re-enabling an
> @@ -1242,10 +1247,8 @@ void msm_drv_shutdown(struct platform_device *pdev)
>         struct msm_drm_private *priv = platform_get_drvdata(pdev);
>         struct drm_device *drm = priv ? priv->dev : NULL;
>
> -       if (!priv || !priv->kms)
> -               return;
> -
> -       drm_atomic_helper_shutdown(drm);
> +       if (drm)
> +               msm_shutdown_hw(drm);
>  }
>
>  static struct platform_driver msm_platform_driver = {
> --
> 2.37.1
>


-- 
With best wishes
Dmitry