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

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Date:	Wed, 27 Aug 2014 03:42:48 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	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 08/27/2014 01:03 AM, David Vrabel wrote:
> 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().
> 

OK, thanks, that sounds reasonable to me, it is not a real wold bug, it
is my fault.  :-)

>> --- 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.
> 

OK, thanks, that sounds reasonable to me.

If necessary to send patch v2 (change comments and contents), please
let me know, and I shall send.

Thanks.
-- 
Chen Gang

Open share and attitude like air water and life which God blessed
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