[Devel] Re: [PATCH] [NETNS45] network namespace locking rules

[Denis V. Lunev]

Daniel, I've sent you last letter from Eric regarding change below. By
the way, you've been in CC: for that thread :)

I'll rebase this to #49 on monday.

Regards,
	Den

Daniel Lezcano wrote:
> Denis V. Lunev wrote:
>> Current locking for network namespace list/initialization is broken.
>> for_each_net is called under single rtnl_lock in
>> register_netdevice_notifier.
>>
>> Locking:
>>     net_mutex -> rtnl_lock() -> dev_base_lock
>> Reasoning:
>>   - net_mutex holds serialization of the addition/removal of
>>     subsystems/modules and the creation/destruction of network
>>     namespaces as a whole
>>   - loopback device is one of such subsystems and it takes
>>     rtnl_lock inside
>>   - per/namespace RTNL netlink socket requires an iteration over
>>     namespace list inside rtnl_unlock, which is called inside net_mutex
>> Resume:
>>     net_namespace_list is guarded by both rtnl_lock & net_mutex and
>>     can be safely iterated under any of them
>>
>> Signed-off-by: Denis V. Lunev <den at openvz.org>
>>
>> --------
> 
> [ cut ]
>>  
>> -void net_lock(void)
>> -{
>> -    mutex_lock(&net_list_mutex);
>> -}
>> -
>> -void net_unlock(void)
>> -{
>> -    mutex_unlock(&net_list_mutex);
>> -}
>> -
> 
> net_list_mutex is no more needed, right ? The removing of its
> declaration is missing (already done in #netns49)
> 
>>  static struct net *net_alloc(void)
>>  {
>>      return kmem_cache_alloc(net_cachep, GFP_KERNEL);
>> @@ -71,9 +62,9 @@ static void cleanup_net(struct work_struct *work)
>>      mutex_lock(&net_mutex);
>>  
>>      /* Don't let anyone else find us. */
>> -    net_lock();
>> +    rtnl_lock();
>>      list_del(&net->list);
>> -    net_unlock();
>> +    rtnl_unlock();
>>  
>>      /* Run all of the network namespace exit methods */
>>      pernet_count = 0;
>> @@ -193,9 +184,9 @@ struct net *copy_net_ns(unsigned long flags,
>> struct net *old_net)
>>      if (err)
>>          goto out_unlock;
>>  
>> -    net_lock();
>> +    rtnl_lock();
>>      list_add_tail(&new_net->list, &net_namespace_list);
>> -    net_unlock();
>> +    rtnl_unlock();
>>  
>>  
>>  out_unlock:
>> @@ -220,14 +211,13 @@ static int __init net_ns_init(void)
>>      mutex_lock(&net_mutex);
>>      err = setup_net(&init_net);
>>  
>> -    net_lock();
>> +    rtnl_lock();
>>      list_add_tail(&init_net.list, &net_namespace_list);
>> -    net_unlock();
>> +    rtnl_unlock();
>>  
>>      mutex_unlock(&net_mutex);
>>      if (err)
>>          panic("Could not setup the initial network namespace");
>> -
>>      return 0;
>>  }
>>  
> 
> Eric did already these changes in #netns49.
> 
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index 82ebc23..e610313 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
>> @@ -73,16 +73,24 @@ void __rtnl_unlock(void)
>>  void rtnl_unlock(void)
>>  {
>>      struct net *net;
>> -    mutex_unlock(&rtnl_mutex);
>> -   
>> -    net_lock();
>> +
>> +retry:
>>      for_each_net(net) {
>>          struct sock *rtnl = net->rtnl;
>> +
>> +        if (rtnl == NULL || rtnl->sk_receive_queue.qlen == 0)
>> +            continue;
>> +
>> +        get_net(net);
>> +        mutex_unlock(&rtnl_mutex);
>>          if (rtnl && rtnl->sk_receive_queue.qlen)
>                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> this statement is always true with the previous one.
> 
>>              rtnl->sk_data_ready(rtnl, 0);
>> -    }
>> -    net_unlock();
>> +        mutex_lock(&rtnl_mutex);
>> +        put_net(net);
>>  
>> +        goto retry;
> 
> Why do you need to return to the beginning of the list ?
> 
>> +    }
>> +    mutex_unlock(&rtnl_mutex);
>>      netdev_run_todo();
>>  }
> 
> Denis, can you explain why this part must be modified ?
> 
> 
> 

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