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Re: [RFC 1/2] netvsc: reference counting fix

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From: Stephen Hemminger <stephen@networkplumber.org>
Date: Sat, 13 Aug 2016 11:35:59 -0700

> This is how I think it should be fixed, but not tested yet.
> 
> Subjec: netvsc: use device not module reference counts
> 
> Fix how the cross-device reference counting is handled.  When VF is
> associated with the synthetic interface, the VF driver module should
> still be able to be unloaded.  The module unload code will callback
> with NETDEV_UNREGISTER event which breaks the connection safely.
> (Fixes 9f4b5ba5db4 hv_netvsc: Implement support for VF drivers on Hyper-V)
> 
> Signed-off-by: Stephen Hemminger <sthemmin@linuxonhyperv.com>

This might not work.

It is assumed that when a netdev unregister happens, it may be done so
at any point in time.

Therefore that NETDEV_UNREGISTER event must eliminate any and all
references to a given netdev.  And that works perfectly fine right now
with all existing subsystems that take references to netdevs.

You'll have to add something so that a NETDEV_UNREGISTER event tears
this VF down and thus releases it's reference to the synthetic device.

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[PATCH net 2/4] hv_netvsc: reset vf_inject on VF removal Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-08-11 13:00 +0200
  RE: [PATCH net 2/4] hv_netvsc: reset vf_inject on VF removal Yuval Mintz <Yuval.Mintz@qlogic.com> - 2016-08-11 13:50 +0200
    Re: [PATCH net 2/4] hv_netvsc: reset vf_inject on VF removal Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-08-11 14:20 +0200
      Re: [PATCH net 2/4] hv_netvsc: reset vf_inject on VF removal Stephen Hemminger <stephen@networkplumber.org> - 2016-08-12 16:50 +0200
  Re: [PATCH net 2/4] hv_netvsc: reset vf_inject on VF removal David Miller <davem@davemloft.net> - 2016-08-13 05:50 +0200
  [RFC 2/2] netvsc: use RCU for VF net device reference Stephen Hemminger <stephen@networkplumber.org> - 2016-08-14 13:20 +0200
    Re: [RFC 2/2] netvsc: use RCU for VF net device reference Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-08-15 12:10 +0200
  [RFC 1/2] netvsc: reference counting fix Stephen Hemminger <stephen@networkplumber.org> - 2016-08-14 13:30 +0200
    Re: [RFC 1/2] netvsc: reference counting fix David Miller <davem@davemloft.net> - 2016-08-15 06:40 +0200

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