linux-kernel - Re: [PATCH] drivers/xen/grant-table.c: Be sure of unsigned value never comparing with 0

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Date:	Tue, 26 Aug 2014 18:03:14 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Chen Gang <gang.chen.5i5j@...il.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>
CC:	<xen-devel@...ts.xenproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/xen/grant-table.c: Be sure of unsigned value
 never comparing with 0

On 26/08/14 16:38, Chen Gang wrote:
> In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may
> be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than
> 'nr_glist_frames' in failure processing, which cause infinite looping.

nr_grant_frames is at least 1.  See gnttab_init().

> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
>  	return 0;
>  
>  grow_nomem:
> -	for ( ; i >= nr_glist_frames; i--)
> -		free_page((unsigned long) gnttab_list[i]);
> +	while (i > nr_glist_frames)
> +		free_page((unsigned long) gnttab_list[--i]);

while (i-- > nr_glist_frames)
    ...

Would have been better.

David
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