linux-kernel - Re: [PATCH 1/1] xen: xenbus: set error code on failure

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Date:   Mon, 5 Dec 2016 07:30:49 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Pan Bian <bianpan2016@....com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Vrabel <david.vrabel@...rix.com>,
        xen-devel@...ts.xenproject.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] xen: xenbus: set error code on failure

On 03/12/16 11:49, Pan Bian wrote:
> In function xenstored_local_init(), the value of return variable err
> should be negative on errors. But the value of err keeps 0 even if the 
> call to get_zeroed_page() returns a NULL pointer. This patch assigns 
> "-ENOMEM" to err on the error branch.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=188721
> 
> Signed-off-by: Pan Bian <bianpan2016@....com>
> ---
>  drivers/xen/xenbus/xenbus_probe.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> index 33a31cf..f87d047 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -708,8 +708,10 @@ static int __init xenstored_local_init(void)
>  
>  	/* Allocate Xenstore page */
>  	page = get_zeroed_page(GFP_KERNEL);
> -	if (!page)
> +	if (!page) {
> +		err = -ENOMEM;
>  		goto out_err;
> +	}
>  
>  	xen_store_gfn = xen_start_info->store_mfn = virt_to_gfn((void *)page);

Why don't you preset err to -ENOMEM instead? Initializing it to 0
is kind of pointless.

Ans while at it: preinitializing page isn't needed, too, and in the
error path testing page for being non-zero isn't neede either
(free_page() will do the right thing in case the parameter is 0).


Juergen