From mboxrd@z Thu Jan  1 00:00:00 1970
From: Namjae Jeon <linkinjeon@gmail.com>
Subject: Re: [PATCH 2/3] writeback: fix incorrect return value type of bdi_dirty_limit
Date: Mon, 20 Aug 2012 08:49:33 +0900
Message-ID: <CAKYAXd_+=s+A4GN0Sgmbb9RO94SQFkAvdLDwuZgRu4LFPLsgQA@mail.gmail.com>
References: <1345283361-7802-1-git-send-email-linkinjeon@gmail.com>
	<20120819021757.GB16796@localhost>
	<5030BE93.50909@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Cc: Fengguang Wu <fengguang.wu@intel.com>, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
To: Marco Stornelli <marco.stornelli@gmail.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <5030BE93.50909@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

2012/8/19, Marco Stornelli <marco.stornelli@gmail.com>:
> Il 19/08/2012 04:17, Fengguang Wu ha scritto:
>> On Sat, Aug 18, 2012 at 05:49:21AM -0400, Namjae Jeon wrote:
>>> unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long
>>> dirty)
>>>
>>> Above function return type is unsigned long, but return value is
>>> kept in "u64 bdi_dirty".
>>> It can return incorrect value by type casting.
>>
>> I don't see how the cast can return wrong value.
>> The u64 is necessary for the intermediate calculations.
>>
>> Thanks,
>> Fengguang
>>
>
> We are sure u64 is 8byte long, but unsigned long is 4byte long on 32-bit
> machine, so if bdi_dirty can assume values bigger than 2^32 there is an
> implicit truncate of its value, isn't it?
Yes, right.
Thanks.
>
> Marco
>