xen-netback: fix a BUG() during initialization

[ Upstream commit 12b322ac85208de564ecf23aa754d796a91de21f ]

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@amazon.de>
Cc: Matt Wilson <msw@amazon.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 968787abf78d..ec383b0f5443 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);