From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH] xen-netfront: remove warning when unloading module
Date: Mon, 20 Nov 2017 10:49:19 +0000
Message-ID: <20171120104919.ziq45hikwbzlnvbo@citrix.com>
References: <20171120104109.11585-1-otubo@redhat.com>
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Cc: <xen-devel@lists.xenproject.org>, <netdev@vger.kernel.org>,
        <paul.durrant@citrix.com>, <wei.liu2@citrix.com>,
        <linux-kernel@vger.kernel.org>, <vkuznets@redhat.com>,
        <cavery@redhat.com>, <cheshi@redhat.com>, <mgamal@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Eduardo Otubo <otubo@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
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In-Reply-To: <20171120104109.11585-1-otubo@redhat.com>
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CC netfront maintainers.

On Mon, Nov 20, 2017 at 11:41:09AM +0100, Eduardo Otubo wrote:
> When unloading module xen_netfront from guest, dmesg would output
> warning messages like below:
> 
>   [  105.236836] xen:grant_table: WARNING: g.e. 0x903 still in use!
>   [  105.236839] deferring g.e. 0x903 (pfn 0x35805)
> 
> This problem relies on netfront and netback being out of sync. By the time
> netfront revokes the g.e.'s netback didn't have enough time to free all of
> them, hence displaying the warnings on dmesg.
> 
> The trick here is to make netfront to wait until netback frees all the g.e.'s
> and only then continue to cleanup for the module removal, and this is done by
> manipulating both device states.
> 
> Signed-off-by: Eduardo Otubo <otubo@redhat.com>
> ---
>  drivers/net/xen-netfront.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 8b8689c6d887..b948e2a1ce40 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -2130,6 +2130,17 @@ static int xennet_remove(struct xenbus_device *dev)
>  
>  	dev_dbg(&dev->dev, "%s\n", dev->nodename);
>  
> +	xenbus_switch_state(dev, XenbusStateClosing);
> +	while (xenbus_read_driver_state(dev->otherend) != XenbusStateClosing){
> +		cpu_relax();
> +		schedule();
> +	}
> +	xenbus_switch_state(dev, XenbusStateClosed);
> +	while (dev->xenbus_state != XenbusStateClosed){
> +		cpu_relax();
> +		schedule();
> +	}
> +
>  	xennet_disconnect_backend(info);
>  
>  	unregister_netdev(info->netdev);
> -- 
> 2.13.6
>