Re: [PATCH 12/14] drm/kmb: Fix possible oops in error handling

[Sam Ravnborg <sam@ravnborg.org>]

Hi Anitha,

On Tue, Jul 27, 2021 at 05:31:24PM -0700, Anitha Chrisanthus wrote:
> If kmb_dsi_init() fails the "kmb->kmb_dsi" variable is an error pointer.
> This can potentially result in kernel panic when kmb_dsi_host_unregister is
> called.
> 
> Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> Fixes: 98521f4d4b4c ("drm/kmb: Mipi DSI part of the display driver")
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>
> ---
>  drivers/gpu/drm/kmb/kmb_drv.c | 9 ++++++---
>  drivers/gpu/drm/kmb/kmb_dsi.c | 9 +++++----
>  drivers/gpu/drm/kmb/kmb_dsi.h | 3 ++-
>  3 files changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/kmb/kmb_drv.c b/drivers/gpu/drm/kmb/kmb_drv.c
> index bb7eca9e13ae..12f35c43d838 100644
> --- a/drivers/gpu/drm/kmb/kmb_drv.c
> +++ b/drivers/gpu/drm/kmb/kmb_drv.c
> @@ -454,8 +454,9 @@ static int kmb_remove(struct platform_device *pdev)
>  	dev_set_drvdata(dev, NULL);
>  
>  	/* Unregister DSI host */
> -	kmb_dsi_host_unregister(kmb->kmb_dsi);
> +	kmb_dsi_host_unregister();
>  	drm_atomic_helper_shutdown(drm);
> +	drm_dev_put(drm);
>  	return 0;
>  }
>  
> @@ -519,7 +520,7 @@ static int kmb_probe(struct platform_device *pdev)
>  	if (IS_ERR(kmb->kmb_dsi)) {
>  		drm_err(&kmb->drm, "failed to initialize DSI\n");
>  		ret = PTR_ERR(kmb->kmb_dsi);
> -		goto err_free1;
> +		goto err_free2;
>  	}
>  
>  	kmb->kmb_dsi->dev = &dsi_pdev->dev;
> @@ -555,8 +556,10 @@ static int kmb_probe(struct platform_device *pdev)
>  	drm_crtc_cleanup(&kmb->crtc);
>  	drm_mode_config_cleanup(&kmb->drm);
>   err_free1:
> +	kmb_dsi_clk_disable(kmb->kmb_dsi);
> + err_free2:
>  	dev_set_drvdata(dev, NULL);
> -	kmb_dsi_host_unregister(kmb->kmb_dsi);
> +	kmb_dsi_host_unregister();
>  

This really looks like a step backward. There should not be a eed to
call unregister if kmb_dsi is not a valid pointer in the first place.
Also drn_dev_put() should not be needed with the use of drmm
infrastructure.



>  	return ret;
>  }
> diff --git a/drivers/gpu/drm/kmb/kmb_dsi.c b/drivers/gpu/drm/kmb/kmb_dsi.c
> index 1cca0fe6f35f..a500172ada87 100644
> --- a/drivers/gpu/drm/kmb/kmb_dsi.c
> +++ b/drivers/gpu/drm/kmb/kmb_dsi.c
> @@ -172,17 +172,17 @@ mipi_hs_freq_range[MIPI_DPHY_DEFAULT_BIT_RATES] = {
>  	{.default_bit_rate_mbps = 2500, .hsfreqrange_code = 0x49}
>  };
>  
> -static void kmb_dsi_clk_disable(struct kmb_dsi *kmb_dsi)
> +void kmb_dsi_clk_disable(struct kmb_dsi *kmb_dsi)
>  {
>  	clk_disable_unprepare(kmb_dsi->clk_mipi);
>  	clk_disable_unprepare(kmb_dsi->clk_mipi_ecfg);
>  	clk_disable_unprepare(kmb_dsi->clk_mipi_cfg);
>  }
>  
> -void kmb_dsi_host_unregister(struct kmb_dsi *kmb_dsi)
> +void kmb_dsi_host_unregister(void)
>  {
> -	kmb_dsi_clk_disable(kmb_dsi);
> -	mipi_dsi_host_unregister(kmb_dsi->host);
> +	if (dsi_host)
> +		mipi_dsi_host_unregister(dsi_host);
>  }
I thought we had killed the global dsi_host variable??
Seems some cleanup is till needed here.

	Sam