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

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Date:	Thu, 07 Oct 2010 11:51:21 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	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()

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.

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.


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