[Devel] Re: cleanup in workq and dst_destroy

[Denis V. Lunev]

Daniel Lezcano wrote:
> Denis V. Lunev wrote:
>> Daniel Lezcano wrote:
>>> Hi all,
>>>
>>> while doing ipv6 namespace, we were faced to a problem with the loopback
>>> and the dst_destroy function.
>>>
>>> When the network namespace exits, the cleanup function is called by
>>> schedule_work and this function will browse the net ops list to call the
>>> different exit methods for the registered subsystems.
>>>
>>> The different subsystems will shutdown their resources and in particular
>>> addrconf subsystem will ifdown the loopback. This function will call
>>> rt6_ifdown
>>>  -> fib6_clean_all
>>>   -> fib6_clean_node
>>>    -> fib6_clean_tree
>>>     -> fib6_clean_node
>>>      -> fib6_del
>>>       -> fib6_del_route
>>>        -> rt6_release
>>>         ->dst_free
>>>          -> __dst_free
>>>
>>> The __dst_free function will schedule_delayed_work the dst_gc_work
>>> function.
>>>
>>> The dst_gc_work will call dst_destroy and finally this one will call
>>> dst->ops->destroy ops function which is ip6_dst_destroy.
>>>
>>> The problem here is we have the workq blocked because we are running
>>> inside the netns cleanup function. So the delayed work will not run
>>> until we exits the cleanup function. But the loopback is still
>>> referenced by the ip6 routes, the netdev_unregister will loop
>>> indefinitly => dead lock.
>>>
>>> By the way, this bug appears with ipv6 but it is perhaps pending with
>>> ipv4.
>>>
>>> Benjamin as proposed to create a separate workq for the network
>>> namespace, so in the worst case we have the unregister looping until the
>>> ip6 route are shut downed. Is it an acceptable solution ?
>>>
>>
>> we are doing this staff in the special thread. There are a lot of
>> difficult things to perform like synchronize_net & netdev_run_todo inside
> 
> The special thread ? do you mean keventd_wq ?
> 
I mean that network namespace deletion, i.e. all subsystem ->exit calls
should be run outside of all current mechanisms in the separate thread,
specially designated to namespace(s) stop.
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