[Devel] Re: net namespace plans for 2.6.25 (was Re: Pid namespaces problems)

[Daniel Lezcano]

Pavel Emelyanov wrote:
> Daniel Lezcano wrote:
>> Denis V. Lunev wrote:
>>  > Daniel Lezcano wrote:
>>  >> Denis V. Lunev wrote:
>>  >>> Daniel Lezcano wrote:
>>  >>>
>>  >>>>  * the first one is the locking of the network namespace list by
>>  >>>> rtnl_lock, so from the timer callback we can not browse the network
>>  >>>> namespace list to check the age of the routes. It is a problem I would
>>  >>>> like to talk with Denis if he has time
>>  >>> From my point of view, the situation is clear. The timer should be
>>  >>> per/namespace. The situation is completely different as one in IPv4.
>>  >> We thought to make a timer per namespace for ipv6, but we are a little
>>  >> afraid for the performances when there will be a lot of containers.
>>  >> Anyway, we can do a timer per namespace and optimize that later. I will
>>  >> cook a new patch to take into account that for the next week.
>>  >
>>  > IMHO not a problem. tcp_write_timer is per/socket timer. If this works
>>  > efficiently, per/namespace one will work also.
>>
>> That's right, this is a good argument. By the way, the amount of work to 
>> be done in the tcp_write_timer is perhaps smaller than the one done in 
>> the ipv6 routing age check, no ? Anyway, I'm not against a timer per 
>> namespace in this case, I already did a try before rolling back to a 
>> for_each_net in the gc timer, that changes a little the API, but nothing 
> 
> We can easily make the netns list rcu protected to address this issue.
> If you're interested, I can prepare a patch tomorrow.

Sure, I'm interested :)

Benjamin and I, we thought about using a rcu to avoid to use a timer per 
namespace in ipv6 but we faced to the problem with rtnl_unlock function 
when the network namespace is protected with the rtnl_lock/rtnl_unlock. 
In the function rtnl_unlock (not the one in net-2.6 but the one which is 
in netns49), there is loop, for_each_net, in this loop, we do 
rtnl_unlock, call sk_data_ready and take the lock again. If we are in 
rcu protected model, this loop will take a lock (one time just before 
sk_data_ready and one time in the sk_data_ready function). As far as I 
understand with rcu, we should not block inside a rcu_read_lock, right ?


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