Re: RDMA subsystem namespace related questions (was Re: Finding the namespace of a struct ib_device)

[Ka-Cheong Poon <ka-cheong.poon@oracle.com>]

On 10/5/20 11:45 PM, Jason Gunthorpe wrote:
> On Mon, Oct 05, 2020 at 11:02:18PM +0800, Ka-Cheong Poon wrote:
>> On 10/5/20 10:25 PM, Jason Gunthorpe wrote:
>>> On Mon, Oct 05, 2020 at 09:57:47PM +0800, Ka-Cheong Poon wrote:
>>>>>> It is a kernel module.  Which FD are you referring to?  It is
>>>>>> unclear why a kernel module must associate itself with a user
>>>>>> space FD.  Is there a particular reason that rdma_create_id()
>>>>>> needs to behave differently than sock_create_kern() in this
>>>>>> regard?
>>>>>
>>>>> Somehow the kernel module has to be commanded to use this namespace,
>>>>> and generally I expect that command to be connected to FD.
>>>>
>>>>
>>>> It is an unnecessary restriction on what a kernel module
>>>> can do.  Is it a problem if a kernel module initiates its
>>>> own RDMA connection for doing various stuff in a namespace?
>>>
>>> Yes, someone has to apply policy to authorize this. Kernel modules
>>> randomly running around using security objects is not OK.
>>
>> The policy is to allow this.  It is not random stuff.
>> Can the RDMA subsystem support it?
> 
> allow everything is not a policy


It is not allowing everything.  It is the simple case that
a kernel module can have a listener without the namespace
issue.  Kernel socket does not have this problem.


>>> Kernel modules should not be doing networking unless commanded to by
>>> userspace.
>>
>> It is still not clear why this is an issue with RDMA
>> connection, but not with general kernel socket.  It is
>> not random networking.  There is a purpose.
> 
> It is a problem with sockets too, how do the socket users trigger
> their socket usages? AFAIK all cases originate with userspace


A user starts a namespace.  The module is loaded for servicing
requests.  The module starts a listener.  The user deletes
the namespace.  This scenario will have everything cleaned up
properly if the listener is a kernel socket.  This is not the
case with RDMA.


>> So if the reason of the current rdma_create_id() behavior
>> is that there is no such user, I am adding one.  It should
>> be clear that this difference between kernel socket and
>> rdma_create_id() causes a problem in namespace handling.
> 
> It would be helpful to understand how that works, as I've said I don't
> think a kernel module should open listening sockets/cm_ids on every
> namespace without being told to do this.


The issue is not about starting a listener.  The issue is on
namespace deletion.




-- 
K. Poon
ka-cheong.poon@oracle.com