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

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Message-ID: <47FF662B.2040302@trash.net>
Date:	Fri, 11 Apr 2008 15:22:51 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Jarek Poplawski <jarkao2@...il.com>
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()

Jarek Poplawski wrote:
> 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?


I'd suggest to behave similar to qdiscs when trying to
removing classes that are still referenced, return -EBUSY.
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