netdev - Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl

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Date:   Thu, 22 Sep 2016 15:41:23 +0200
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

On 22.09.2016 15:03, Eric Dumazet wrote:
> On Thu, 2016-09-22 at 13:03 +0200, Hannes Frederic Sowa wrote:
>> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
>> ---
>>  net/core/net_namespace.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
>> index 2c2eb1b629b11d..a2ace299f28355 100644
>> --- a/net/core/net_namespace.c
>> +++ b/net/core/net_namespace.c
>> @@ -758,9 +758,11 @@ static int __init net_ns_init(void)
>>  
>>  	register_pernet_subsys(&net_ns_ops);
>>  
>> +	rtnl_lock();
>>  	rtnl_register(PF_UNSPEC, RTM_NEWNSID, rtnl_net_newid, NULL, NULL);
>>  	rtnl_register(PF_UNSPEC, RTM_GETNSID, rtnl_net_getid, rtnl_net_dumpid,
>>  		      NULL);
>> +	rtnl_unlock();
>>  
>>  	return 0;
>>  }
> 
> Hi Hannes
> 
> Why is this needed here, and not in other places ?

I found this during working on the file and actually saw no live issues
(belonged to another series which I just split up).

I don't think it is a big issue but wanted the writes to the
rtnl_msg_handlers array to be strictly serialized. I was working on
adding this to other places, too. Maybe better for net-next even?

Theoretically we would need to add a memory barriers to make sure we
don't publish uninitialized memory into the array if concurrent readers
of the array want to find their function pointers.

> Hint : A changelog always help reviewers and future bug hunting.

I will add that to v2.

Thanks,
Hannes