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Date: Fri, 12 Aug 2016 07:47:27 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Yuval Mintz <Yuval.Mintz@qlogic.com>, netdev <netdev@vger.kernel.org>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>
Subject: Re: [PATCH net 2/4] hv_netvsc: reset vf_inject on VF removal
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On Thu, 11 Aug 2016 14:09:53 +0200
Vitaly Kuznetsov <vkuznets@redhat.com> wrote:

> Yuval Mintz <Yuval.Mintz@qlogic.com> writes:
> 
> >> +static void netvsc_inject_enable(struct net_device_context
> >> +*net_device_ctx) {
> >> +	net_device_ctx->vf_inject = true;
> >> +}
> >> +
> >> +static void netvsc_inject_disable(struct net_device_context
> >> +*net_device_ctx) {
> >> +	net_device_ctx->vf_inject = false;
> >> +
> >> +	/* Wait for currently active users to drain out. */
> >> +	while (atomic_read(&net_device_ctx->vf_use_cnt) != 0)
> >> +		udelay(50);
> >> +}  
> >
> > That was already the behavior before, but are you certain you
> > want to unconditionally block without any possible timeout?  
> 
> Yes, this is OK. After PATCH4 of this series there is only one place
> which takes the vf_use_cnt (netvsc_recv_callback()) and it is an
> interrupt handler, there are no sleepable operations there.
> 

Since network devices are protected by RCU, it looks like the refcount
is not necessary.  I think vf_inject flag and vf_use_cnt could just be replaced
by doing RCU on vf_netdev.

The callback is invoked from tasklet (softirq) context.