Message-ID: <5030C17E.5050906@gmail.com>
Date: Sun, 19 Aug 2012 12:35:42 +0200
From: Marco Stornelli <marco.stornelli@gmail.com>
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To: Fengguang Wu <fengguang.wu@intel.com>
CC: Namjae Jeon <linkinjeon@gmail.com>, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/3] writeback: fix incorrect return value type of bdi_dirty_limit
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Il 19/08/2012 12:23, Marco Stornelli ha scritto:
> 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?
>
> Marco

Sorry but I didn't see the code, it seems not possible so the wrong 
situation can't happen. Maybe we can simply add a comment, nothing more.

Marco
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