netdev - Re: [PATCH net-next 5/6] netns: use a spin

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Message-ID: <554A19CD.2070608@6wind.com>
Date:	Wed, 06 May 2015 15:40:29 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Thomas Graf <tgraf@...g.ch>
CC:	netdev@...r.kernel.org, davem@...emloft.net, ebiederm@...ssion.com
Subject: Re: [PATCH net-next 5/6] netns: use a spin_lock to protect nsid management

Le 06/05/2015 14:23, Thomas Graf a écrit :
> On 05/06/15 at 11:58am, Nicolas Dichtel wrote:
>> +/* Should be called with nsid_lock held. If a new id is assigned, the bool alloc
>> + * is set to true, thus the caller knows that the new id must be notified via
>> + * rtnl.
>> + */
>>   static int __peernet2id(struct net *net, struct net *peer, bool *alloc)
>>   {
>>   	int id = idr_for_each(&net->netns_ids, net_eq_idr, peer);
>>   	bool alloc_it = *alloc;
>>
>> -	ASSERT_RTNL();
>> -
>>   	*alloc = false;
>>
>>   	/* Magic value for id 0. */
>
> If split into __peernet2id() and __peernet2id_alloc() then this could
> live with RCU protection I guess so we only take the lock when we
> actually allocate.
>
The description of idr_for_each says:
"The caller must serialize idr_for_each() vs idr_get_new() and idr_remove()."

So, if I understand well, the lock is always needed.
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