[dpdk-dev] [PATCH v2 02/10] kni: separate releasing netdev from freeing KNI interface

Dan Gora dg at adax.com
Wed Oct 10 20:18:14 CEST 2018

On Wed, Oct 10, 2018 at 2:25 PM Ferruh Yigit <ferruh.yigit at intel.com> wrote:
> On 9/4/2018 1:36 AM, Dan Gora wrote:
> > Hi Ferruh,
> >
> > I remembered now the motivation behind separating rte_kni_release()
> > and rte_kni_free().
> >
> > The problem is that the DPDK thread which calls rte_kni_release()
> > _cannot_ be the same thread which handles callbacks from the KNI
> > driver via rte_kni_handle_request().  This is because the thread which
> > calls rte_kni_release() will be stuck down in
> > ioctl(RTE_KNI_IOCTL_RELEASE) when the kernel calls the
> > RTE_KNI_REQ_CFG_NETWORK_IF callback to the DPDK application.  Since
> > that thread cannot call rte_kni_handle_request(), the callback would
> > then just timeout unless some other thread calls
> > rte_kni_handle_request().
> >
> > So then you are in a bit of a chicken and egg situation.  You _have_
> > to have a separate thread calling rte_kni_handle_request periodically,
> > but that thread also _cannot_ run after rte_kni_release returns
> > (actually it's worse than that because it's actually after the
> > ioctl(RTE_KNI_IOCTL_RELEASE) returns and the fifos are freed).
> I see, so we have problem in both end, -userspace side and kernel side.
> Agreed that separating release & free may help, but I am not sure about adding a
> new API for KNI.
> Very simply, what about prevent kni_net_release() send callback to userspace?

No, because how is the DPDK application going to know when the user
does 'ip link set down dev <kniX>'?   It's important for the DPDK
application to know when the KNI interface is marked down.

> This is already not working and removing it resolves the issues you mentioned.

Huh?  How is it not working?  Of course it works.

> Sample application calls rte_eth_dev_stop() after release itself, so behavior
> will be same.


> But the issues in kernel you mentioned, using `dev` after free_netdev() called
> should be addressed.

Yes, that's why I fixed them in the patches that I sent.


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