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

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Date:   Mon,  5 Dec 2016 15:50:50 +0800
From:   Pan Bian <bianpan2016@....com>
To:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Vrabel <david.vrabel@...rix.com>,
        xen-devel@...ts.xenproject.org
Cc:     PanBian <bianpan2016@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] xen: xenbus: set error code on failure

From: PanBian <bianpan2016@....com>

On Mon, Dec 05, 2016 at 07:30:49AM +0100, Juergen Gross wrote:
> 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.

  I think presetting and setting on demand are both effective to fix
  this bug. Nevertheless, I will resubmit a second version if you
  insist.

> 
> 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
> 

Thanks!

Best regards,
Pan