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

[Chrisanthus, Anitha]

Hi Sam,

> -----Original Message-----
> From: Sam Ravnborg <sam at ravnborg.org>
> Sent: Wednesday, July 28, 2021 12:27 AM
> To: Chrisanthus, Anitha <anitha.chrisanthus at intel.com>
> Cc: dri-devel at lists.freedesktop.org; Dea, Edmund J
> <edmund.j.dea at intel.com>; Dan Carpenter <dan.carpenter at oracle.com>
> Subject: Re: [PATCH 12/14] drm/kmb: Fix possible oops in error handling
> 
> 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 at oracle.com>
> > Signed-off-by: Anitha Chrisanthus <anitha.chrisanthus at 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.
Agree, I was trying to address issues with Dan's original patch.
I will keep the original code, with only this change
        if (IS_ERR(kmb->kmb_dsi)) {
                drm_err(&kmb->drm, "failed to initialize DSI\n");
-               ret = PTR_ERR(kmb->kmb_dsi);
-               goto err_free2;
+               dev_set_drvdata(dev, NULL);
+               return PTR_ERR(kmb->kmb_dsi);
Will send v2
> 
> 
> 
> >  	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