Subject: [PATCH 09/21] xen-netback: fix a BUG() during initialization

From: "Palik, Imre" <[email-masked]>
Date: Fri, 19 Jun 2015 14:21:51 +0200

[ 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 <[email-masked]>
Cc: Matt Wilson <[email-masked]>
Acked-by: Wei Liu <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 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);
 
-- 
2.1.0