Re: [PATCH] xen-netback: fix memory leaks on XenBus disconnect

On 13/01/17 10:38, Wei Liu wrote:

On Thu, Jan 12, 2017 at 05:51:56PM +0000, Igor Druzhinin wrote:

quoted

Eliminate memory leaks introduced several years ago by cleaning the queue
resources which are allocated on XenBus connection event. Namely, queue
structure array and pages used for IO rings.
vif->lock is used to protect statistics gathering agents from using the
queue structure during cleaning.

There is code in netback_remove which eventually calls xenvif_free to
free up the resources, maybe you should modify xenvif_free instead? That
seems more symmetric to me. What do you think?

quoted

Signed-off-by: Igor Druzhinin <redacted>
---
 drivers/net/xen-netback/interface.c |  6 ++++--
 drivers/net/xen-netback/xenbus.c    | 13 +++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index e30ffd2..5795213 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c

@@ -221,18 +221,18 @@ static struct net_device_stats *xenvif_get_stats(struct net_device *dev)
 {
 	struct xenvif *vif = netdev_priv(dev);
 	struct xenvif_queue *queue = NULL;
-	unsigned int num_queues = vif->num_queues;
 	unsigned long rx_bytes = 0;
 	unsigned long rx_packets = 0;
 	unsigned long tx_bytes = 0;
 	unsigned long tx_packets = 0;
 	unsigned int index;
 
+	spin_lock(&vif->lock);
 	if (vif->queues == NULL)
 		goto out;
 
 	/* Aggregate tx and rx stats from each queue */
-	for (index = 0; index < num_queues; ++index) {
+	for (index = 0; index < vif->num_queues; ++index) {
 		queue = &vif->queues[index];
 		rx_bytes += queue->stats.rx_bytes;
 		rx_packets += queue->stats.rx_packets;

@@ -241,6 +241,8 @@ static struct net_device_stats *xenvif_get_stats(struct net_device *dev)
 	}
 
 out:
+	spin_unlock(&vif->lock);
+

Good catch, this is definitely needed. And it would probably be in a
separate patch.

I suggest we also need to have this spinlock acquired in another part
of cleaning code (xenvif_free). The reason to introduce it is a locking
practice in openvswitch when they don't grab any network subsystem locks
(rtnl_lock) in order to gather the statistics. I'm not sure that it's
correct behavior. Anyone can advise?

Wei.