Re: [RFC 1/7] drm/omap: Use devm_kzalloc() to allocate omap_drm_private

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Peter,

Thank you for the patch.

On Tuesday, 29 August 2017 10:32:12 EEST Peter Ujfalusi wrote:
> It makes the cleanup paths a bit cleaner.

But it also goes against a proper implementation of object lifetime management 
:-( In DRM driver private structures are accessible from file operations, and 
must thus be reference-counted and only freed when the last userspace user 
goes away. This may be after the devm_* resources are released right after the 
.remove() operation is called. Using devm_kzalloc() would thus make it 
impossible to properly reference-count our data structures.

> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
> ---
>  drivers/gpu/drm/omapdrm/omap_drv.c | 19 +++++++------------
>  1 file changed, 7 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c
> b/drivers/gpu/drm/omapdrm/omap_drv.c index 9b3c36b48356..903510d8054e
> 100644
> --- a/drivers/gpu/drm/omapdrm/omap_drv.c
> +++ b/drivers/gpu/drm/omapdrm/omap_drv.c
> @@ -548,19 +548,17 @@ static int pdev_probe(struct platform_device *pdev)
>  		return ret;
>  	}
> 
> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
>  	omap_crtc_pre_init();
> 
>  	ret = omap_connect_dssdevs();
>  	if (ret)
>  		goto err_crtc_uninit;
> 
> -	/* Allocate and initialize the driver private structure. */
> -	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> -	if (!priv) {
> -		ret = -ENOMEM;
> -		goto err_disconnect_dssdevs;
> -	}
> -
> +	/* Initialize the driver private structure. */
>  	priv->dispc_ops = dispc_get_ops();
> 
>  	soc = soc_device_match(omapdrm_soc_devices);
> @@ -574,7 +572,7 @@ static int pdev_probe(struct platform_device *pdev)
>  	ddev = drm_dev_alloc(&omap_drm_driver, &pdev->dev);
>  	if (IS_ERR(ddev)) {
>  		ret = PTR_ERR(ddev);
> -		goto err_free_priv;
> +		goto err_destroy_wq;
>  	}
> 
>  	ddev->dev_private = priv;
> @@ -624,10 +622,8 @@ static int pdev_probe(struct platform_device *pdev)
>  err_free_drm_dev:
>  	omap_gem_deinit(ddev);
>  	drm_dev_unref(ddev);
> -err_free_priv:
> +err_destroy_wq:
>  	destroy_workqueue(priv->wq);
> -	kfree(priv);
> -err_disconnect_dssdevs:
>  	omap_disconnect_dssdevs();
>  err_crtc_uninit:
>  	omap_crtc_pre_uninit();
> @@ -659,7 +655,6 @@ static int pdev_remove(struct platform_device *pdev)
>  	drm_dev_unref(ddev);
> 
>  	destroy_workqueue(priv->wq);
> -	kfree(priv);
> 
>  	omap_disconnect_dssdevs();
>  	omap_crtc_pre_uninit();


-- 
Regards,

Laurent Pinchart

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