netdev - Re: [PATCH net-next] openvswitch: fix vport-netdev unregister

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Date:	Fri, 11 Oct 2013 11:11:39 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Pravin Shelar <pshelar@...ira.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Pirko <jiri@...nulli.us>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] openvswitch: fix vport-netdev unregister

On Thu, Oct 10, 2013 at 9:48 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
> On Thu, Oct 10, 2013 at 8:56 PM, Jesse Gross <jesse@...ira.com> wrote:
>> However, the check dev->reg_state in netdev_destroy() looks racy to
>> me, as it could already be in NETREG_UNREGISTERED even if we already
>> processed this device.
>
> you mean that netdev_destroy() will see reg_state == netreg_unregistered,
> while dp_device_event() didn't see reg_state == netreg_unregistering yet?
> or dp_device_event() saw it, proceeded to do unlink and
> netdev_destroy() ran in parallel?
> well, that's why reg_state == netreg_unregistering check in netdev_destroy()
> is done with rtnl_lock() held.
> reg_state cannot go into netreg_unregistered state skipping
> netreg_unregistering and notifier.
> therefore I don't think it's racy.
>
> In ovs_dp_notify_wq() you're checking for both unregistering and
> unregistered and that makes
> sense, since workq can run after unregistering notifier called and
> netdev_run_todo()
> already changed the state to unregistered.
> But here it's not the case.

ovs_dp_notify_wq() calls ovs_dp_detach_port(), which indirectly calls
netdev_destroy() so it seems like it actually is the same case to me.
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