Re: [PATCH] netfilter: add locking for counters zeroing

[Patrick McHardy <kaber@trash.net>]

Jan Engelhardt wrote:
> On Wednesday 2008-09-24 12:01, Patrick McHardy wrote:
>>> @@ -545,6 +545,7 @@ ctnetlink_dump_table(struct sk_buff *skb, struct
>>> netlink_callback *cb)
>>>   u_int8_t l3proto = nfmsg->nfgen_family;
>>>  
>>> 	rcu_read_lock();
>>> +	spin_lock_bh(&nf_conntrack_lock);
>> We only need the spinlock. I'm not so happy about taking it
>> unconditionally even though we might not be zeroing the
>> counters. Moving it in the inner loop will greatly increase
>> the amount of locks/unlocks on the other hand.
>>
>> How about moving the inner loop to a new function and adding
>> back the ctnetlink_dump_counterzero (or whatever it was called)
>> function? It would take the spinlock, while normal dumping
>> would only use rcu_read_lock().
> 
> Perhaps this might work?
> 
> +	if (cb->args[0] >= nf_conntrack_htable_size) {
> +		nf_ct_put(cb->args[1]);
> +		return skb->len;
> +	}

I'm not sure what you're trying to fix here. Its a race
between counter zeroing and changing them during packet
processing. Any patch that doesn't include a spin_lock
can't really fix the problem :)