linux-kernel - Re: [PATCH] mm: nobootmem: avoid type warning about alignment value

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Date:	Mon, 9 Dec 2013 20:02:30 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] mm: nobootmem: avoid type warning about alignment value

On Monday 09 December 2013 07:54 PM, Russell King - ARM Linux wrote:
> On Mon, Dec 09, 2013 at 04:50:44PM -0800, Andrew Morton wrote:
>> On Mon, 25 Nov 2013 08:57:54 -0500 Santosh Shilimkar <santosh.shilimkar@...com> wrote:
>>
>>> On Sunday 24 November 2013 10:14 AM, Sergei Shtylyov wrote:
>>>> Hello.
>>>>
>>>> On 24-11-2013 3:28, Santosh Shilimkar wrote:
>>>>
>>>>> Building ARM with NO_BOOTMEM generates below warning. Using min_t
>>>>
>>>>    Where is that below? :-)
>>>>
>>> Damn.. Posted a wrong version of the patch ;-(
>>> Here is the one with warning message included.
>>>
>>> >From 571dfdf4cf8ac7dfd50bd9b7519717c42824f1c3 Mon Sep 17 00:00:00 2001
>>> From: Santosh Shilimkar <santosh.shilimkar@...com>
>>> Date: Sat, 23 Nov 2013 18:16:50 -0500
>>> Subject: [PATCH] mm: nobootmem: avoid type warning about alignment value
>>>
>>> Building ARM with NO_BOOTMEM generates below warning.
>>>
>>> mm/nobootmem.c: In function _____free_pages_memory___:
>>> mm/nobootmem.c:88:11: warning: comparison of distinct pointer types lacks a cast
>>>
>>> Using min_t to find the correct alignment avoids the warning.
>>>
>>> Cc: Tejun Heo <tj@...nel.org>
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...com>
>>> ---
>>>  mm/nobootmem.c |    2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/nobootmem.c b/mm/nobootmem.c
>>> index 2c254d3..8954e43 100644
>>> --- a/mm/nobootmem.c
>>> +++ b/mm/nobootmem.c
>>> @@ -85,7 +85,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
>>>  	int order;
>>>  
>>>  	while (start < end) {
>>> -		order = min(MAX_ORDER - 1UL, __ffs(start));
>>> +		order = min_t(size_t, MAX_ORDER - 1UL, __ffs(start));
>>>  
>>
>> size_t makes no sense.  Neither `order', `MAX_ORDER', 1UL nor __ffs()
>> have that type.
>>
>> min() warnings often indicate that the chosen types are inappropriate,
>> and suppressing them with min_t() should be a last resort.
>>
>> MAX_ORDER-1UL has type `unsigned long' (yes?) and __ffs() should return
>> unsigned long (except arch/arc which decided to be different).
>>
>> Why does it warn?  What's the underlying reason?
> 
> The underlying reason is that - as I've already explained - ARM's __ffs()
> differs from other architectures in that it ends up being an int, whereas
> almost everyone else is unsigned long.
> 
> The fix is to fix ARMs __ffs() to conform to other architectures.
> 
I was just about to cross-post your reply here. Obviously I didn't think
this far when I made  $subject fix.

So lets ignore the $subject patch which is not correct. Sorry for noise

Regards,
Santosh




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