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

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Date:   Fri, 13 Jan 2017 10:38:00 +0000
From:   Wei Liu <wei.liu2@...rix.com>
To:     Igor Druzhinin <igor.druzhinin@...rix.com>
CC:     <wei.liu2@...rix.com>, <xen-devel@...ts.xenproject.org>,
        <paul.durrant@...rix.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen-netback: fix memory leaks on XenBus disconnect

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

> Signed-off-by: Igor Druzhinin <igor.druzhinin@...rix.com>
> ---
>  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.

Wei.