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

From: "Palik, Imre" <imrep@xxxxxxxxx>

Commit edafc132baac ("xen-netback: making the bandwidth limiter runtime 
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>
 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);

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