Re: [PATCH 4.4 105/124] xen-netfront: wait xenbus state change when load module manually

[Ben Hutchings]

On Sat, 2018-08-04 at 11:01 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.ÂÂIf anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Xiao Liang <xiliang@xxxxxxxxxx>
> 
> [ Upstream commit 822fb18a82abaf4ee7058793d95d340f5dab7bfc ]
> 
> When loading module manually, after call xenbus_switch_state to initializes
> the state of the netfront device, the driver state did not change so fast
> that may lead no dev created in latest kernel. This patch adds wait to make
> sure xenbus knows the driver is not in closed/unknown state.
[...]
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -86,6 +86,7 @@ struct netfront_cb {
> Â/* IRQ name is queue name with "-tx" or "-rx" appended */
> Â#define IRQ_NAME_SIZE (QUEUE_NAME_SIZE + 3)
> Â
> +static DECLARE_WAIT_QUEUE_HEAD(module_load_q);
> Âstatic DECLARE_WAIT_QUEUE_HEAD(module_unload_q);
> Â
> Âstruct netfront_stats {
> @@ -1335,6 +1336,11 @@ static struct net_device *xennet_create_
> Â	netif_carrier_off(netdev);
> Â
> Â	xenbus_switch_state(dev, XenbusStateInitialising);
> +	wait_event(module_load_q,
> +			ÂÂÂxenbus_read_driver_state(dev->otherend) !=
> +			ÂÂÂXenbusStateClosed &&
> +			ÂÂÂxenbus_read_driver_state(dev->otherend) !=
> +			ÂÂÂXenbusStateUnknown);
> Â	return netdev;
> Â
> Â exit:

This won't work; it will hang.  Something (maybe netback_changed()?)
needs to wake up tasks on the module_load_q.

Ben.

-- 
Ben Hutchings, Software Developer                Â        Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
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