From mboxrd@z Thu Jan  1 00:00:00 1970
From: Patrick McHardy <kaber@trash.net>
Subject: Re: [PATCH 3/3] nfnetlink_queue: use hash table to speed up entry
 	finding.
Date: Fri, 16 Apr 2010 17:30:26 +0200
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Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	netfilter-devel@vger.kernel.org
To: Changli Gao <xiaosuo@gmail.com>
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Changli Gao wrote:
> On Thu, Apr 15, 2010 at 11:35 PM, Patrick McHardy <kaber@trash.net> wrote:
>> Changli Gao wrote:
>>> static int
>>> nfqnl_rcv_nl_event(struct notifier_block *this,
>>>                    unsigned long event, void *ptr)
>>> {
>>>         struct netlink_notify *n = ptr;
>>>
>>>         if (event == NETLINK_URELEASE && n->protocol == NETLINK_NETFILTER) {
>>>                 int i;
>>>
>>>                 /* destroy all instances for this pid */
>>>                 spin_lock(&instances_lock);
>>>                 for (i = 0; i < INSTANCE_BUCKETS; i++) {
>>>                         struct hlist_node *tmp, *t2;
>>>                         struct nfqnl_instance *inst;
>>>                         struct hlist_head *head = &instance_table[i];
>>>
>>>                         hlist_for_each_entry_safe(inst, tmp, t2, head, hlist) {
>>>                                 if ((n->net == &init_net) &&
>>>                                     (n->pid == inst->peer_pid))
>>>                                         __instance_destroy(inst);
>>>                         }
>>>                 }
>>>                 spin_unlock(&instances_lock);
>>>         }
>>>         return NOTIFY_DONE;
>>> }
>>>
>>> static struct notifier_block nfqnl_rtnl_notifier = {
>>>         .notifier_call  = nfqnl_rcv_nl_event,
>>> };
>>>
>> Ah, right. So call nfnl_lock() or convert the spinlock to a
>> mutex.
>>
> 
> We can't convert the spinlock to a mutex simply. The notifier chain is
> an atomic notifier chain.

Well, then use reference counting, redo the lookup, or whatever.
Really, this isn't that hard.