netdev - Re: [PATCH] sysctl: fix min/max handling in __do_proc_doulongvec

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Message-ID: <20101008161344.GG4088@hack>
Date:	Sat, 9 Oct 2010 00:13:44 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Robin Holt <holt@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Willy Tarreau <w@....eu>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	James Morris <jmorris@...ei.org>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	Patrick McHardy <kaber@...sh.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>, ebiederm@...ssion.com
Subject: Re: [PATCH] sysctl: fix min/max handling in
	__do_proc_doulongvec_minmax()

On Thu, Oct 07, 2010 at 11:51:21AM +0200, Eric Dumazet wrote:
>Le jeudi 07 octobre 2010 à 17:25 +0800, Américo Wang a écrit :
>> >>
>> >
>> >Here is the final one.
>> 
>> Oops, that one is not correct. Hopefully this one
>> is correct.
>> 
>> --------------->
>> 
>> Eric D. noticed that we may trigger an OOPS if we leave ->extra{1,2}
>> to NULL when we use proc_doulongvec_minmax().
>> 
>> Actually, we don't need to store min/max values in a vector,
>> because all the elements in the vector should share the same min/max
>> value, like what proc_dointvec_minmax() does.
>> 
>
>If we assert same min/max limits are to be applied to all elements,
>a much simpler fix than yours would be :
>
>diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>index f88552c..8e45451 100644
>--- a/kernel/sysctl.c
>+++ b/kernel/sysctl.c
>@@ -2485,7 +2485,7 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
> 		kbuf[left] = 0;
> 	}
> 
>-	for (; left && vleft--; i++, min++, max++, first=0) {
>+	for (; left && vleft--; i++, first=0) {
> 		unsigned long val;
> 
> 		if (write) {
>
>
>Please dont send huge patches like this to 'fix' a bug,
>especially on slow path.

Well, my patch makes that horrible code a little better. :)

>
>First we fix the bug, _then_ we can try to make code more 
>efficient or more pretty or shorter.
>
>So the _real_ question is :
>
>Should the min/max limits should be a single pair,
>shared by all elements, or a vector of limits.
>

Yes, actually I talked with Eric W. about this before
sending the patch.

I also checked the users of proc_doulongvec_minmax(),
none of them are using more than one limit, so it is
safe to remove that.


-- 
Live like a child, think like the god.
 
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