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From: Paul Durrant <xadimgnik@gmail.com>
To: Michael Brown <mbrown@fensystems.co.uk>,
	xen-devel@lists.xenproject.org, netdev@vger.kernel.org,
	wei.liu@kernel.org, pdurrant@amazon.com
Subject: Re: [PATCH] xen-netback: Check for hotplug-status existence before watching
Date: Tue, 13 Apr 2021 20:12:35 +0100	[thread overview]
Message-ID: <8bd038a2-b870-4f9b-733d-77efe7b9afe1@xen.org> (raw)
In-Reply-To: <20210413152512.903750-1-mbrown@fensystems.co.uk>

On 13/04/2021 16:25, Michael Brown wrote:
> The logic in connect() is currently written with the assumption that
> xenbus_watch_pathfmt() will return an error for a node that does not
> exist.  This assumption is incorrect: xenstore does allow a watch to
> be registered for a nonexistent node (and will send notifications
> should the node be subsequently created).
> 
> As of commit 1f2565780 ("xen-netback: remove 'hotplug-status' once it
> has served its purpose"), this leads to a failure when a domU
> transitions into XenbusStateConnected more than once.  On the first
> domU transition into Connected state, the "hotplug-status" node will
> be deleted by the hotplug_status_changed() callback in dom0.  On the
> second or subsequent domU transition into Connected state, the
> hotplug_status_changed() callback will therefore never be invoked, and
> so the backend will remain stuck in InitWait.
> 
> This failure prevents scenarios such as reloading the xen-netfront
> module within a domU, or booting a domU via iPXE.  There is
> unfortunately no way for the domU to work around this dom0 bug.
> 
> Fix by explicitly checking for existence of the "hotplug-status" node,
> thereby creating the behaviour that was previously assumed to exist.
> 
> Signed-off-by: Michael Brown <mbrown@fensystems.co.uk>

Reviewed-by: Paul Durrant <paul@xen.org>

> ---
>   drivers/net/xen-netback/xenbus.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
> index a5439c130130..d24b7a7993aa 100644
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -824,11 +824,15 @@ static void connect(struct backend_info *be)
>   	xenvif_carrier_on(be->vif);
>   
>   	unregister_hotplug_status_watch(be);
> -	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch, NULL,
> -				   hotplug_status_changed,
> -				   "%s/%s", dev->nodename, "hotplug-status");
> -	if (!err)
> +	if (xenbus_exists(XBT_NIL, dev->nodename, "hotplug-status")) {
> +		err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
> +					   NULL, hotplug_status_changed,
> +					   "%s/%s", dev->nodename,
> +					   "hotplug-status");
> +		if (err)
> +			goto err;
>   		be->have_hotplug_status_watch = 1;
> +	}
>   
>   	netif_tx_wake_all_queues(be->vif->dev);
>   
> 



  reply	other threads:[~2021-04-13 19:12 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-10 18:25 xen-netback hotplug-status regression bug Michael Brown
2021-04-13  7:12 ` Paul Durrant
2021-04-13 10:48   ` Michael Brown
2021-04-13 10:55     ` Paul Durrant
2021-04-13 15:14       ` Michael Brown
2021-04-13 15:25       ` [PATCH] xen-netback: Check for hotplug-status existence before watching Michael Brown
2021-04-13 19:12         ` Paul Durrant [this message]
2021-04-13 22:30         ` patchwork-bot+netdevbpf
2021-05-10 18:32         ` Marek Marczykowski-Górecki
2021-05-10 18:47           ` Michael Brown
2021-05-10 18:53             ` Marek Marczykowski-Górecki
2021-05-10 19:06               ` Michael Brown
2021-05-10 19:42                 ` Marek Marczykowski-Górecki
2021-05-11  7:06                   ` Durrant, Paul
2021-05-11 10:40                     ` Marek Marczykowski-Górecki
2021-05-11 10:45                       ` Marek Marczykowski-Górecki
2021-05-11 12:46                         ` Durrant, Paul
2021-05-17 21:43                           ` Marek Marczykowski-Górecki
2021-05-17 21:51                             ` Michael Brown
2021-05-17 21:58                               ` Marek Marczykowski-Górecki
2021-05-18  6:57                             ` Paul Durrant
2021-05-18  9:18                               ` Marek Marczykowski-Górecki
     [not found]                                 ` <887f9533f5c54bfabfbff7231eb99b08@EX13D32EUC003.ant.amazon.com>
     [not found]                                   ` <YKOMpXwcnr9QiXy8@mail-itl>
     [not found]                                     ` <2c23e102b6254e42877eb1e8fe68a4f7@EX13D32EUC003.ant.amazon.com>
2021-05-18 10:42                                       ` Marek Marczykowski-Górecki

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