netdev - Re: [PATCH][NET_SCHED] cls_u32: refcounting fix for u32

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Message-ID: <20080411132304.GB2701@ff.dom.local>
Date:	Fri, 11 Apr 2008 13:23:04 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	David Miller <davem@...emloft.net>,
	Jamal Hadi Salim <hadi@...erus.ca>, netdev@...r.kernel.org
Subject: Re: [PATCH][NET_SCHED] cls_u32: refcounting fix for u32_delete()

On Fri, Apr 11, 2008 at 02:55:27PM +0200, Patrick McHardy wrote:
> Jarek Poplawski wrote:
>> [NET_SCHED] cls_u32: refcounting fix for u32_delete()
>>
>> @@ -441,8 +443,10 @@ static int u32_delete(struct tcf_proto *tp, unsigned long arg)
>>  	if (tp->root == ht)
>>  		return -EINVAL;
>>  -	if (--ht->refcnt == 0)
>> +	if (ht->refcnt == 1) {
>> +		ht->refcnt--;
>>  		u32_destroy_hnode(tp, ht);
>> +	}
>>  
>
> Shouldn't the refcount be decremented unconditionally?
> Otherwise I'd suggest to reject the removal if refcnt > 1,
> but silently doing nothing doesn't seem right.

If someone tries deleting and the refcnt is e.g. 3 (2 links)
unconditional deleting could decrease refcnt without deleting
and then unlinking would make it below 0. I think it's OK now:
we can't delete hnode until it's referenced, but I could add
a warning if you like?

Thanks,
Jarek P.
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