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

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Message-ID: <1536689787.3024.130.camel@codethink.co.uk>
Date:   Tue, 11 Sep 2018 19:16:27 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        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 Fri, 2018-09-07 at 13:27 -0400, Boris Ostrovsky wrote:
> 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

Thanks.

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
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