netdev - Re: [PATCH 2/14][NETNS]: Generic per-net pointers.

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Date:	Fri, 11 Apr 2008 18:29:13 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Daniel Lezcano <dlezcano@...ibm.com>
CC:	Linux Netdev List <netdev@...r.kernel.org>,
	Denis Lunev <den@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	Benjamin Thery <benjamin.thery@...l.net>
Subject: Re: [PATCH 2/14][NETNS]: Generic per-net pointers.

[snip]

>> @@ -29,10 +32,21 @@ static __net_init int setup_net(struct net *net)
>>  	/* Must be called with net_mutex held */
>>  	struct pernet_operations *ops;
>>  	int error;
>> +	struct net_generic *ng;
>>
>>  	atomic_set(&net->count, 1);
>>  	atomic_set(&net->use_count, 0);
>>
>> +	error = -ENOMEM;
>> +	ng = kzalloc(sizeof(struct net_generic) +
>> +			INITIAL_NET_GEN_PTRS * sizeof(void *), GFP_KERNEL);
> 
> Why do you need to allocate more than sizeof(struct net_generic) ?

That's just an optimization to avoid many reallocations in the
nearest future. I planned to make similar in net_assign_generic
(allocate a bit more that required), but decided to do it later
to keep net_assign_generic simpler.

Currently I have only 5 users of generic pointers (tun and vlan
you see and I have patches for ipip, ipgre and sit tunnels), so
that's enough for the first time.

[snip]

>> +int net_assign_generic(struct net *net, int id, void *data)
>> +{
>> +	struct net_generic *ng, *old_ng;
>> +
>> +	BUG_ON(!mutex_is_locked(&net_mutex));
>> +	BUG_ON(id == 0);
>> +
>> +	ng = old_ng = net->gen;
> 
> shouldn't it be rcu_dereferenced ?

Nope - nobody can race with us and change this pointer, so it's
safe to get one without rcu_dereference.

Thanks,
Pavel
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