netdev - Re: [PATCH] conntrack: use SLAB_DESTROY_BY_RCU for nf

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Message-ID: <49CA76C4.2090409@trash.net>
Date:	Wed, 25 Mar 2009 19:24:04 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	mbizon@...ebox.fr, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>,
	avorontsov@...mvista.com, netdev@...r.kernel.org,
	Netfilter Developers <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH] conntrack: use SLAB_DESTROY_BY_RCU for nf_conn structs

Eric Dumazet wrote:
> Patrick McHardy a écrit :
>>> +static struct hlist_nulls_node *ct_get_first(struct seq_file *seq)
>>>  {
>>>      struct net *net = seq_file_net(seq);
>>>      struct ct_iter_state *st = seq->private;
>>> -    struct hlist_node *n;
>>> +    struct hlist_nulls_node *n;
>>>  
>>>      for (st->bucket = 0;
>>>           st->bucket < nf_conntrack_htable_size;
>>>           st->bucket++) {
>>>          n = rcu_dereference(net->ct.hash[st->bucket].first);
>>> -        if (n)
>>> +        if (!is_a_nulls(n))
>>>              return n;
>>>      }
>>>      return NULL;
>>>  }
>> Don't we need to make sure the entry is not reused while dumping
>> it?
>>
> 
> Ah yes, I forgot that for UDP/TCP I had to change locking on this part.
> Because messing with reference count was crazy...
> But in UDP/TCP we have different spinlock for each chain, so hold time
> was small enough.
> 
> So I guess that with central conntrack lock, we need to take references on entries
> while dumping them.

Yes, I think so too.
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