linux-kernel - Re: [Xen-devel] [PATCH] pvcalls-front: fixes incorrect error handling

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Date:   Tue, 27 Nov 2018 08:58:23 +0800
From:   PanBian <bianpan2016@....com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] pvcalls-front: fixes incorrect error handling

On Mon, Nov 26, 2018 at 03:31:39PM -0500, Boris Ostrovsky wrote:
> On 11/21/18 9:07 PM, Pan Bian wrote:
> > kfree() is incorrectly used to release the pages allocated by
> > __get_free_page() and __get_free_pages(). Use the matching deallocators
> > i.e., free_page() and free_pages(), respectively.
> >
> > Signed-off-by: Pan Bian <bianpan2016@....com>
> > ---
> >  drivers/xen/pvcalls-front.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index 2f11ca7..77224d8 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -385,8 +385,8 @@ static int create_active(struct sock_mapping *map, int *evtchn)
> >  out_error:
> >  	if (*evtchn >= 0)
> >  		xenbus_free_evtchn(pvcalls_front_dev, *evtchn);
> > -	kfree(map->active.data.in);
> > -	kfree(map->active.ring);
> > +	free_pages((unsigned long)map->active.data.in, PVCALLS_RING_ORDER);
> 
> Is map->active.data.in guaranteed to be NULL when entering this routine?

I am not sure yet. Sorry for that. I observed the mismatches between
__get_free_page and kfree, and submitted the patch.

But I think your consideration is reasonable. A better solution is to
directly free bytes, a local variable that holds __get_free_pages return
value. If you agree, I will rewrite the patch.

Thanks,
Pan

> 
> -boris
> 
> > +	free_page((unsigned long)map->active.ring);
> >  	return ret;
> >  }
> >  
>