netdev - Re: [PATCH net-next v2 1/2] inetpeer: add namespace support for inetpeer

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Date:	Tue, 05 Jun 2012 20:29:35 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	serge.hallyn@...onical.com, ebiederm@...ssion.com,
	herbert@...dor.apana.org.au, steffen.klassert@...unet.com,
	davem@...emloft.net, netdev@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v2 1/2] inetpeer: add namespace support for inetpeer

于 2012年06月05日 16:57, Eric Dumazet 写道:
> On Tue, 2012-06-05 at 15:52 +0800, Gao feng wrote:
> 
>> +static void __net_exit inetpeer_net_exit(struct net *net)
>> +{
>> +	inetpeer_invalidate_tree(net, AF_INET);
>> +	kfree(net->ipv4.peers);
>> +
>> +	inetpeer_invalidate_tree(net, AF_INET6);
>> +	kfree(net->ipv6.peers);
>> +}
>> +
> 
> Are we 1000% sure no code ever run in inetpeer land after this call ?

I am not sure,I need more time to research it.
I just do kfree peers here without set NULL pointer is
beacuse there is the same code with fib6_main_tbl in fib6_net_exit
and it seems work well.

Anyway, I will research it.

> 
> I would add
> 	net->ipv4.peers = NULL;
> 	net->ipv6.peers = NULL;
> 
> to catch NULL deref instead of strange errors, just in case.
> 
> By the way, I think we have a bug in inetpeer_gc_worker()
> 
> Steffen ?
> 
> We have no rcu grace period to make sure the following is safe :
> 
> if (!atomic_read(&p->refcnt)) {
> 	list_del(&p->gc_list);
> 	kmem_cache_free(peer_cachep, p);
> }
> 
> I'll post a fix like :
> 
> diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
> index d4d61b6..07731b5 100644
> --- a/net/ipv4/inetpeer.c
> +++ b/net/ipv4/inetpeer.c
> @@ -137,7 +137,7 @@ static void inetpeer_gc_worker(struct work_struct *work)
>  
>  		n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
>  
> -		if (!atomic_read(&p->refcnt)) {
> +		if (atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
>  			list_del(&p->gc_list);
>  			kmem_cache_free(peer_cachep, p);
>  		}
> 
> 
> 
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