Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero
To:     zhong jiang <zhongjiang@huawei.com>, akpm@linux-foundation.org,
        mhocko@kernel.org
Cc:     anshuman.khandual@arm.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Ira Weiny <ira.weiny@intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
References: <1567592763-25282-1-git-send-email-zhongjiang@huawei.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <5505fa16-117e-8890-0f48-38555a61a036@suse.cz>
Date:   Wed, 4 Sep 2019 13:24:58 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <1567592763-25282-1-git-send-email-zhongjiang@huawei.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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).

> Signed-off-by: zhong jiang <zhongjiang@huawei.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.

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;
>  		}
>