[PATCH] drm: mxsfb: Fix NULL pointer dereference crash on unload

[Daniel Vetter]

On Tue, Sep 07, 2021 at 04:49:00AM +0200, Marek Vasut wrote:
> The mxsfb->crtc.funcs may already be NULL when unloading the driver,
> in which case calling mxsfb_irq_disable() via drm_irq_uninstall() from
> mxsfb_unload() leads to NULL pointer dereference.
> 
> Since all we care about is masking the IRQ and mxsfb->base is still
> valid, just use that to clear and mask the IRQ.
> 
> Fixes: ae1ed00932819 ("drm: mxsfb: Stop using DRM simple display pipeline helper")
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Daniel Abrecht <public at danielabrecht.ch>
> Cc: Emil Velikov <emil.l.velikov at gmail.com>
> Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: Stefan Agner <stefan at agner.ch>

You probably want a drm_atomic_helper_shutdown instead of trying to do all
that manually. We've also added a bunch more devm and drmm_ functions to
automate the cleanup a lot more here, e.g. your drm_mode_config_cleanup is
in the wrong place.

Also I'm confused because I'm not even seeing this function anywhere in
upstream.
-Daniel

> ---
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index ec0432fe1bdf8..86d78634a9799 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -173,7 +173,11 @@ static void mxsfb_irq_disable(struct drm_device *drm)
>  	struct mxsfb_drm_private *mxsfb = drm->dev_private;
>  
>  	mxsfb_enable_axi_clk(mxsfb);
> -	mxsfb->crtc.funcs->disable_vblank(&mxsfb->crtc);
> +
> +	/* Disable and clear VBLANK IRQ */
> +	writel(CTRL1_CUR_FRAME_DONE_IRQ_EN, mxsfb->base + LCDC_CTRL1 + REG_CLR);
> +	writel(CTRL1_CUR_FRAME_DONE_IRQ, mxsfb->base + LCDC_CTRL1 + REG_CLR);
> +
>  	mxsfb_disable_axi_clk(mxsfb);
>  }
>  
> -- 
> 2.33.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch