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From: Hans Verkuil <hverkuil@xs4all.nl>
To: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>,
	Robert Foss <robert.foss@linaro.org>,
	Todor Tomov <todor.too@gmail.com>
Cc: Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v2] media: camss: Allocate camss struct as a managed device resource
Date: Thu, 19 May 2022 09:16:36 +0200	[thread overview]
Message-ID: <2a813aab-424d-bc88-fb69-e9bbe9104736@xs4all.nl> (raw)
In-Reply-To: <20220519051415.1198248-1-vladimir.zapolskiy@linaro.org>

Robert, Vladimir,

On 5/19/22 07:14, Vladimir Zapolskiy wrote:
> The change simplifies driver's probe and remove functions, no functional
> change is intended.
> 
> Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
> ---
> Changes from v1 to v2:
> * rebased on top of media/master
> 
>  drivers/media/platform/qcom/camss/camss.c | 33 +++++++----------------
>  1 file changed, 10 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> index 79ad82e233cb..2055233af101 100644
> --- a/drivers/media/platform/qcom/camss/camss.c
> +++ b/drivers/media/platform/qcom/camss/camss.c
> @@ -1529,7 +1529,7 @@ static int camss_probe(struct platform_device *pdev)
>  	struct camss *camss;
>  	int num_subdevs, ret;
>  
> -	camss = kzalloc(sizeof(*camss), GFP_KERNEL);
> +	camss = devm_kzalloc(dev, sizeof(*camss), GFP_KERNEL);

In general it is not a good idea to use devm_*alloc. The problem is that if a
device instance is forcibly unbound, then all the memory allocated with devm_
is immediately freed. But if an application still has a file handle to a device
open, then it can still use that memory.

Now in this case the driver is already using devm_kcalloc, so it doesn't matter,
but it is something to keep in mind. In general, hotpluggable devices cannot use
devm_*alloc.

In general, my recommendation is to not use devm_*alloc for this, but since it
is already in use in this driver, it's better to use devm_*alloc consistently.
Or, alternatively, not use it all. That's up to Robert.

This is just as background information.

Regards,

	Hans

>  	if (!camss)
>  		return -ENOMEM;
>  
> @@ -1567,39 +1567,30 @@ static int camss_probe(struct platform_device *pdev)
>  		camss->csid_num = 4;
>  		camss->vfe_num = 4;
>  	} else {
> -		ret = -EINVAL;
> -		goto err_free;
> +		return -EINVAL;
>  	}
>  
>  	camss->csiphy = devm_kcalloc(dev, camss->csiphy_num,
>  				     sizeof(*camss->csiphy), GFP_KERNEL);
> -	if (!camss->csiphy) {
> -		ret = -ENOMEM;
> -		goto err_free;
> -	}
> +	if (!camss->csiphy)
> +		return -ENOMEM;
>  
>  	camss->csid = devm_kcalloc(dev, camss->csid_num, sizeof(*camss->csid),
>  				   GFP_KERNEL);
> -	if (!camss->csid) {
> -		ret = -ENOMEM;
> -		goto err_free;
> -	}
> +	if (!camss->csid)
> +		return -ENOMEM;
>  
>  	if (camss->version == CAMSS_8x16 ||
>  	    camss->version == CAMSS_8x96) {
>  		camss->ispif = devm_kcalloc(dev, 1, sizeof(*camss->ispif), GFP_KERNEL);
> -		if (!camss->ispif) {
> -			ret = -ENOMEM;
> -			goto err_free;
> -		}
> +		if (!camss->ispif)
> +			return -ENOMEM;
>  	}
>  
>  	camss->vfe = devm_kcalloc(dev, camss->vfe_num, sizeof(*camss->vfe),
>  				  GFP_KERNEL);
> -	if (!camss->vfe) {
> -		ret = -ENOMEM;
> -		goto err_free;
> -	}
> +	if (!camss->vfe)
> +		return -ENOMEM;
>  
>  	v4l2_async_nf_init(&camss->notifier);
>  
> @@ -1681,8 +1672,6 @@ static int camss_probe(struct platform_device *pdev)
>  	v4l2_device_unregister(&camss->v4l2_dev);
>  err_cleanup:
>  	v4l2_async_nf_cleanup(&camss->notifier);
> -err_free:
> -	kfree(camss);
>  
>  	return ret;
>  }
> @@ -1709,8 +1698,6 @@ void camss_delete(struct camss *camss)
>  		device_link_del(camss->genpd_link[i]);
>  		dev_pm_domain_detach(camss->genpd[i], true);
>  	}
> -
> -	kfree(camss);
>  }
>  
>  /*

  reply	other threads:[~2022-05-19  7:16 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-19  5:14 Vladimir Zapolskiy
2022-05-19  7:16 ` Hans Verkuil [this message]
2022-05-23  9:26   ` Robert Foss

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