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

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Date:   Fri, 07 Sep 2018 01:21:22 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Xiao Liang <xiliang@...hat.com>
Cc:     stable@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 105/124] xen-netfront: wait xenbus state change when
 load module manually

On Sat, 2018-08-04 at 11:01 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Xiao Liang <xiliang@...hat.com>
> 
> [ 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 {
>  /* IRQ name is queue name with "-tx" or "-rx" appended */
>  #define IRQ_NAME_SIZE (QUEUE_NAME_SIZE + 3)
>  
> +static DECLARE_WAIT_QUEUE_HEAD(module_load_q);
>  static DECLARE_WAIT_QUEUE_HEAD(module_unload_q);
>  
>  struct netfront_stats {
> @@ -1335,6 +1336,11 @@ static struct net_device *xennet_create_
>  	netif_carrier_off(netdev);
>  
>  	xenbus_switch_state(dev, XenbusStateInitialising);
> +	wait_event(module_load_q,
> +			   xenbus_read_driver_state(dev->otherend) !=
> +			   XenbusStateClosed &&
> +			   xenbus_read_driver_state(dev->otherend) !=
> +			   XenbusStateUnknown);
>  	return netdev;
>  
>   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                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom