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

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Date:   Fri, 7 Sep 2018 13:27:08 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        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>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH 4.4 105/124] xen-netfront: wait xenbus state change when
 load module manually

On 09/06/2018 08:21 PM, Ben Hutchings wrote:
> 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.


https://lkml.org/lkml/2018/9/7/691


-boris