linux-kernel - Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

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Date:   Thu, 5 Sep 2019 10:05:04 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     <akpm@...ux-foundation.org>, <mhocko@...nel.org>,
        <anshuman.khandual@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Ira Weiny <ira.weiny@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

On 2019/9/4 19:24, Vlastimil Babka wrote:
> On 9/4/19 12:26 PM, zhong jiang wrote:
>> With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
>> compare with zero. And __get_user_pages_locked will return an long value.
>> Hence, Convert the long to compare with zero is feasible.
> It would be nicer if the parameter nr_pages was long again instead of unsigned
> long (note there are two variants of the function, so both should be changed).
Yep, the parameter 'nr_pages' was changed to long. and the variants ‘i、step’ should
be changed accordingly.
>> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
> Fixes: 932f4a630a69 ("mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM")
>
> (which changed long to unsigned long)
>
> AFAICS... stable shouldn't be needed as the only "risk" is that we goto
> check_again even when we fail, which should be harmless.
Agreed, Thanks.

Sincerely,
zhong jiang
> Vlastimil
>
>> ---
>>  mm/gup.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 23a9f9c..956d5a1 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1508,7 +1508,7 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
>>  						   pages, vmas, NULL,
>>  						   gup_flags);
>>  
>> -		if ((nr_pages > 0) && migrate_allow) {
>> +		if (((long)nr_pages > 0) && migrate_allow) {
>>  			drain_allow = true;
>>  			goto check_again;
>>  		}
>>
>
> .
>