linux-kernel - Re: [PATCH 3/3] usb: gadget: f_hid: tidy error handling in hidg

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Date:   Wed, 23 Nov 2022 13:19:35 +0100
From:   Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To:     John Keeping <john@...anate.com>, linux-usb@...r.kernel.org
Cc:     Fabien Chouteau <fabien.chouteau@...co.com>,
        Peter Korsgaard <peter.korsgaard@...co.com>,
        Felipe Balbi <balbi@...com>,
        Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lee Jones <lee@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 3/3] usb: gadget: f_hid: tidy error handling in hidg_alloc

W dniu 22.11.2022 o 13:35, John Keeping pisze:
> Unify error handling at the end of the function, reducing the risk of
> missing something on one of the error paths.
> 
> Moving the increment of opts->refcnt later means there is no need to
> decrement it on the error path and is safe as this is guarded by
> opts->lock which is held for this entire section.
> 
> Signed-off-by: John Keeping <john@...anate.com>

Reviewed-by: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
> ---
>   drivers/usb/gadget/function/f_hid.c | 21 +++++++++++----------
>   1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
> index 6be6009f911e..a8da3b4a2855 100644
> --- a/drivers/usb/gadget/function/f_hid.c
> +++ b/drivers/usb/gadget/function/f_hid.c
> @@ -1269,18 +1269,14 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
>   	opts = container_of(fi, struct f_hid_opts, func_inst);
>   
>   	mutex_lock(&opts->lock);
> -	++opts->refcnt;
>   
>   	device_initialize(&hidg->dev);
>   	hidg->dev.release = hidg_release;
>   	hidg->dev.class = hidg_class;
>   	hidg->dev.devt = MKDEV(major, opts->minor);
>   	ret = dev_set_name(&hidg->dev, "hidg%d", opts->minor);
> -	if (ret) {
> -		--opts->refcnt;
> -		mutex_unlock(&opts->lock);
> -		return ERR_PTR(ret);
> -	}
> +	if (ret)
> +		goto err_unlock;
>   
>   	hidg->bInterfaceSubClass = opts->subclass;
>   	hidg->bInterfaceProtocol = opts->protocol;
> @@ -1291,14 +1287,13 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
>   						 opts->report_desc_length,
>   						 GFP_KERNEL);
>   		if (!hidg->report_desc) {
> -			put_device(&hidg->dev);
> -			--opts->refcnt;
> -			mutex_unlock(&opts->lock);
> -			return ERR_PTR(-ENOMEM);
> +			ret = -ENOMEM;
> +			goto err_put_device;
>   		}
>   	}
>   	hidg->use_out_ep = !opts->no_out_endpoint;
>   
> +	++opts->refcnt;
>   	mutex_unlock(&opts->lock);
>   
>   	hidg->func.name    = "hid";
> @@ -1313,6 +1308,12 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
>   	hidg->qlen	   = 4;
>   
>   	return &hidg->func;
> +
> +err_put_device:
> +	put_device(&hidg->dev);
> +err_unlock:
> +	mutex_unlock(&opts->lock);
> +	return ERR_PTR(ret);
>   }
>   
>   DECLARE_USB_FUNCTION_INIT(hid, hidg_alloc_inst, hidg_alloc);