Re: [Xen-devel] [PATCH] xen-netfront: wait xenbus state change when load module manually

From: Jiri Slaby
Date: Fri Aug 24 2018 - 07:13:03 EST

On 07/30/2018, 10:18 AM, Xiao Liang wrote:
> On 07/29/2018 11:30 PM, David Miller wrote:
>> From: Xiao Liang <xiliang@xxxxxxxxxx>
>> Date: Fri, 27 Jul 2018 17:56:08 +0800
>>> @@ -1330,6 +1331,11 @@ static struct net_device
>>> *xennet_create_dev(struct xenbus_device *dev)
>>> ÂÂÂÂÂ netif_carrier_off(netdev);
>>> Â ÂÂÂÂÂ xenbus_switch_state(dev, XenbusStateInitialising);
>>> +ÂÂÂ wait_event(module_load_q,
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ xenbus_read_driver_state(dev->otherend) !=
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ XenbusStateClosed &&
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ xenbus_read_driver_state(dev->otherend) !=
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ XenbusStateUnknown);
>>> ÂÂÂÂÂ return netdev;
>>> Â ÂÂ exit:
>> What performs the wakeups that will trigger for this sleep site?
> In my understanding, backend leaving closed/unknow state can trigger the
> wakeups. I mean to make sure both sides are ready for creating connection.

While backporting this to 4.12, I was surprised by the commit the same
as Boris and David.

So I assume the explanation is that wake_up_all of module_unload_q in
netback_changed wakes also all the processes waiting on module_load_q?
If so, what makes sure that module_unload_q is queued and the process is
the same as for module_load_q?

To me, it looks rather error-prone. Unless it is erroneous now, at least
for future changes. Wouldn't it make sense to wake up module_load_q
along with module_unload_q in netback_changed? Or drop module_load_q
completely and use only module_unload_q (i.e. in xennet_create_dev too)?

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