linux-kernel - Re: [PATCH] kernel: sysctl: use 'unsigned long' type for 'zero' variable

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Date:	Thu, 04 Dec 2014 07:12:45 +0100
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>
CC:	Dmitry Vyukov <dvyukov@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Nadia.Derbey@...l.net, aquini@...hat.com, davidlohr@...com,
	Joe Perches <joe@...ches.com>, avagin@...nvz.org,
	LKML <linux-kernel@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] kernel: sysctl: use 'unsigned long' type for 'zero' variable

Hi Andrew,

On 12/04/2014 12:25 AM, Andrew Morton wrote:
> On Wed, 03 Dec 2014 15:41:21 +0300 Andrey Ryabinin <a.ryabinin@...sung.com> wrote:
>
>> Use the 'unsigned long' type for 'zero' variable to fix this.
>> Changing type to 'unsigned long' shouldn't affect any other users
>> of this variable.
>>
>> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
>> Fixes: ed4d4902ebdd ("mm, hugetlb: remove hugetlb_zero and hugetlb_infinity")
>> Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>
>> ---
>>   kernel/sysctl.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 15f2511..45c45c9 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -120,7 +120,7 @@ static int sixty = 60;
>>   
>>   static int __maybe_unused neg_one = -1;
>>   
>> -static int zero;
>> +static unsigned long zero;
>>   static int __maybe_unused one = 1;
>>   static int __maybe_unused two = 2;
>>   static int __maybe_unused four = 4;
> Yeah, this is ghastly.
>
> Look at
>
> 	{
> 		.procname	= "numa_balancing",
> 		.data		= NULL, /* filled in by handler */
> 		.maxlen		= sizeof(unsigned int),
> 		.mode		= 0644,
> 		.proc_handler	= sysctl_numa_balancing,
> 		.extra1		= &zero,
> 		.extra2		= &one,
> 	},
>
> Now extra1 points at a long and extra2 points at an int.
> sysctl_numa_balancing() calls proc_dointvec_minmax() and I think your
> patch just broke big-endian 64-bit machines.  "sched_autogroup_enabled"
> breaks as well.
What about getting rid of "extra1" and "extra2" as well and replace it 
with "min" and "max"?
I've attached an idea

> and change proc_dointvec_minmax() and a million other functions to take
> `union sysctl_payload *' arguments.  But I haven't thought about it much.
Another idea: why do we pass "int *" instead of "int"?

With "int", we could use
     .int_min = 0;
     .int_max = 1;


--
     Manfred

View attachment "0001-PATCH-Allow-type-safe-documented-sysctl.patch" of type "text/x-patch" (4369 bytes)