linux-kernel - Re: [PATCH] sunvdc: Balance device refcount in vdc_port_mpgroup

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Message-ID: <20af2368-beb4-4b99-bf53-a773aee92744@onemain.com>
Date: Fri, 18 Jul 2025 10:09:01 -0700
From: Shannon Nelson <sln@...main.com>
To: Ma Ke <make24@...as.ac.cn>, axboe@...nel.dk, Jim.Quigley@...cle.com,
 liam.merwick@...cle.com, aaron.young@...cle.com, alexandre.chartre@...cle.com
Cc: akpm@...ux-foundation.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] sunvdc: Balance device refcount in vdc_port_mpgroup_check

On 7/18/25 1:22 AM, Ma Ke wrote:
> Using device_find_child() to locate a probed virtual-device-port node
> causes a device refcount imbalance, as device_find_child() internally
> calls get_device() to increment the device’s reference count before
> returning its pointer. vdc_port_mpgroup_check() directly returns true
> upon finding a matching device without releasing the reference via
> put_device(). We should call put_device() to decrement refcount.
>
> As comment of device_find_child() says, 'NOTE: you will need to drop
> the reference with put_device() after use'.
>
> Found by code review.
>
> Cc: stable@...r.kernel.org
> Fixes: 3ee70591d6c4 ("sunvdc: prevent sunvdc panic when mpgroup disk added to guest domain")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
>   drivers/block/sunvdc.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/sunvdc.c b/drivers/block/sunvdc.c
> index b5727dea15bd..b6dbd5dd2723 100644
> --- a/drivers/block/sunvdc.c
> +++ b/drivers/block/sunvdc.c
> @@ -950,6 +950,7 @@ static bool vdc_port_mpgroup_check(struct vio_dev *vdev)
>   {
>   	struct vdc_check_port_data port_data;
>   	struct device *dev;
> +	bool found = false;
>   
>   	port_data.dev_no = vdev->dev_no;
>   	port_data.type = (char *)&vdev->type;
> @@ -957,10 +958,12 @@ static bool vdc_port_mpgroup_check(struct vio_dev *vdev)
>   	dev = device_find_child(vdev->dev.parent, &port_data,
>   				vdc_device_probed);
>   
> -	if (dev)
> -		return true;
> +	if (dev) {
> +		found = true;
> +		put_device(dev);
> +	}
>   
> -	return false;
> +	return found;

Don't bother with adding the extra bits just to get a single point of 
exit: keep with the existing style and keep the change simple.

if (dev) {
     put_device(dev);
     return true;
}

(and why am I getting copied on a block device change?)

sln



>   }
>   
>   static int vdc_port_probe(struct vio_dev *vdev, const struct vio_device_id *id)