linux-kernel - Re: [PATCH 1/6] Drivers: hv: kvp: fix IP Failover

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Date:	Thu, 31 Mar 2016 13:19:02 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>, olaf@...fle.de,
	jasowang@...hat.com, linux-kernel@...r.kernel.org,
	apw@...onical.com, devel@...uxdriverproject.org
Subject: Re: [PATCH 1/6] Drivers: hv: kvp: fix IP Failover

On Tue, Mar 29, 2016 at 02:27:16PM +0200, Vitaly Kuznetsov wrote:
> "K. Y. Srinivasan" <kys@...rosoft.com> writes:
> 
> > From: Vitaly Kuznetsov <vkuznets@...hat.com>
> >
> > Hyper-V VMs can be replicated to another hosts and there is a feature to
> > set different IP for replicas, it is called 'Failover TCP/IP'. When
> > such guest starts Hyper-V host sends it KVP_OP_SET_IP_INFO message as soon
> > as we finish negotiation procedure. The problem is that it can happen (and
> > it actually happens) before userspace daemon connects and we reply with
> > HV_E_FAIL to the message. As there are no repetitions we fail to set the
> > requested IP.
> >
> > Solve the issue by postponing our reply to the negotiation message till
> > userspace daemon is connected. We can't wait too long as there is a
> > host-side timeout (cca. 75 seconds) and if we fail to reply in this time
> > frame the whole KVP service will become inactive. The solution is not
> > ideal - if it takes userspace daemon more than 60 seconds to connect
> > IP Failover will still fail but I don't see a solution with our current
> > separation between kernel and userspace parts.
> >
> > Other two modules (VSS and FCOPY) don't require such delay, leave them
> > untouched.
> >
> > Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> 
> An issue was found with this patch: we don't cancel
> kvp_host_handshake_work on module unload and if the work is still
> pending we end up crashing. As far as I can see this series didn't make
> it to char-misc tree so instead of sending a patch to this patch I'll
> send v2 for the original issue.
> 
> Sorry for the inconvenience.

Ok, I'll drop this whole series.  K.Y., can you resend this series after
fixing this up?

thanks,

greg k-h