Re: [Xen-devel] [PATCH] xen-netback: fix a BUG() during initialization

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jun 19, 2015 at 02:21:51PM +0200, Imre Palik wrote:
> From: "Palik, Imre" <imrep@xxxxxxxxx>
> 
> Commit edafc132baac ("xen-netback: making the bandwidth limiter runtime 
> settable")
> introduced the capability to change the bandwidth rate limit at runtime.
> But it also introduced a possible crashing bug.
> 
> If netback receives two XenbusStateConnected without getting the
> hotplug-status watch firing in between, then it will try to register the
> watches for the rate limiter again.  But this triggers a BUG() in the watch
> registration code.
> 
> The fix modifies connect() to remove the possibly existing packet-rate
> watches before trying to install those watches.  This behaviour is in line
> with how connect() deals with the hotplug-status watch.
> 
> Signed-off-by: Imre Palik <imrep@xxxxxxxxx>
> Cc: Matt Wilson <msw@xxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

> ---
>  drivers/net/xen-netback/xenbus.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/xen-netback/xenbus.c 
> b/drivers/net/xen-netback/xenbus.c
> index 968787a..ec383b0 100644
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -681,6 +681,9 @@ static int xen_register_watchers(struct xenbus_device 
> *dev, struct xenvif *vif)
>       char *node;
>       unsigned maxlen = strlen(dev->nodename) + sizeof("/rate");
>  
> +     if (vif->credit_watch.node)
> +             return -EADDRINUSE;
> +
>       node = kmalloc(maxlen, GFP_KERNEL);
>       if (!node)
>               return -ENOMEM;
> @@ -770,6 +773,7 @@ static void connect(struct backend_info *be)
>       }
>  
>       xen_net_read_rate(dev, &credit_bytes, &credit_usec);
> +     xen_unregister_watchers(be->vif);
>       xen_register_watchers(dev, be->vif);
>       read_xenbus_vif_flags(be);
>  
> -- 
> 1.7.9.5

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