[PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[Hannes Frederic Sowa]

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.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;
 }
-- 
2.7.4

Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[Eric Dumazet]

On Thu, 2016-09-22 at 13:03 +0200, Hannes Frederic Sowa wrote:
> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.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 ?

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

Thanks.

Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[Hannes Frederic Sowa]

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@stressinduktion.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

Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[Eric Dumazet]

On Thu, 2016-09-22 at 15:41 +0200, Hannes Frederic Sowa wrote:

> 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?

Sure, and you probably could enforce an ASSERT_RTNL() in rtnl_register()
to catch all offenders.

Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[Cong Wang]

On Thu, Sep 22, 2016 at 6:41 AM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> 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@stressinduktion.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?

But they are called during boot, why is it possible to have a parallel
reader/writer at that time?

Re: [PATCH net] net: rtnl_register in net_ns_init need rtnl_lock

[Hannes Frederic Sowa]

On Thu, Sep 22, 2016, at 19:20, Cong Wang wrote:
> > 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?
> 
> But they are called during boot, why is it possible to have a parallel
> reader/writer at that time?

It also happens during module load time, which isn't synchronized with
rtnl_lock.

Bye,
Hannes