linux-kernel - Re: [PATCH 1/3] ipuv3-crtc: add remove action for devres data

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Message-ID: <1554220163.2338.2.camel@pengutronix.de>
Date:   Tue, 02 Apr 2019 17:49:23 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Michael Grzeschik <m.grzeschik@...gutronix.de>, airlied@...ux.ie,
        gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        dri-devel@...ts.freedesktop.org, rafael@...nel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH 1/3] ipuv3-crtc: add remove action for devres data

Hi Michael,

On Tue, 2019-04-02 at 15:49 +0200, Michael Grzeschik wrote:
> The destroy function in drm_mode_config_cleanup will remove the objects
> in ipu-drm-core by calling its destroy functions if the bind function
> fails. The drm_crtc is also part of the devres allocated ipu_crtc
> object. The ipu_crtc object will already be cleaned up if the bind for
> the crtc fails. This leads drm_crtc_cleanup try to clean already freed
> memory.
> 
> We fix this issue by adding the devres action ipu_crtc_remove_head which
> will remove its head from the objects in ipu-drm-core which then never
> calls its destroy function anymore.
> 
> Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> ---
>  drivers/gpu/drm/imx/ipuv3-crtc.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/imx/ipuv3-crtc.c b/drivers/gpu/drm/imx/ipuv3-crtc.c
> index ec3602ebbc1cd..fa1ee33a43d77 100644
> --- a/drivers/gpu/drm/imx/ipuv3-crtc.c
> +++ b/drivers/gpu/drm/imx/ipuv3-crtc.c
> @@ -429,6 +429,14 @@ static int ipu_crtc_init(struct ipu_crtc *ipu_crtc,
>  	return ret;
>  }
>  
> +static void ipu_crtc_remove_head(void *data)
> +{
> +	struct ipu_crtc *ipu_crtc = data;
> +	struct drm_crtc *crtc = &ipu_crtc->base;
> +
> +	list_del(&crtc->head);

I don't think reaching into drm_crtc internals like this is going to be
robust. Currently, this is either missing the rest of drm_crtc_cleanup,
or it will crash if drm_crtc_init_with_planes hasn't been called yet.

I think you could call devm_add_action with a function that calls
drm_crtc_cleanup after drm_crtc_init_with_planes in ipu_crtc_init.

Alternatively, the ipu_crtc allocation could be changed to kzalloc. It
would then have to freed manually in the drm_crtc_funcs->destroy
callback.

regards
Philipp