Re: [Xen-devel] [PATCH net v3] xen-netback: bookkeep number of active queues in our own module

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 23 June 2014 10:50
> To: xen-devel@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> Cc: boris.ostrovsky@xxxxxxxxxx; Wei Liu; Ian Campbell; Paul Durrant
> Subject: [PATCH net v3] xen-netback: bookkeep number of active queues in
> our own module
> 
> The original code uses netdev->real_num_tx_queues to bookkeep number
> of
> queues and invokes netif_set_real_num_tx_queues to set the number of
> queues. However, netif_set_real_num_tx_queues doesn't allow
> real_num_tx_queues to be smaller than 1, which means setting the number
> to 0 will not work and real_num_tx_queues is untouched.
> 
> This is bogus when xenvif_free is invoked before any number of queues is
> allocated. That function needs to iterate through all queues to free
> resources. Using the wrong number of queues results in NULL pointer
> dereference.
> 
> So we bookkeep the number of queues in xen-netback to solve this
> problem. This fixes a regression introduced by multiqueue patchset in
> 3.16-rc1.
> 
> There's another bug in original code that the real number of RX queues
> is never set. In current Xen multiqueue design, the number of TX queues
> and RX queues are in fact the same. We need to set the numbers of TX and
> RX queues to the same value.
> 
> Also remove xenvif_select_queue and leave queue selection to core
> driver, as suggested by David Miller.
> 
> Reported-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> Change since v2:
> * improve commit message
> ---
>  drivers/net/xen-netback/common.h    |    1 +
>  drivers/net/xen-netback/interface.c |   49 
> ++++++++---------------------------
>  drivers/net/xen-netback/xenbus.c    |   28 ++++++++++----------
>  3 files changed, 26 insertions(+), 52 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-
> netback/common.h
> index 4dd7c4a..2532ce8 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -222,6 +222,7 @@ struct xenvif {
> 
>       /* Queues */
>       struct xenvif_queue *queues;
> +     unsigned int num_queues; /* active queues, resource allocated */
> 
>       /* Miscellaneous private stuff. */
>       struct net_device *dev;
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-
> netback/interface.c
> index 852da34..9e97c7c 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -137,32 +137,11 @@ static void xenvif_wake_queue_callback(unsigned
> long data)
>       }
>  }
> 
> -static u16 xenvif_select_queue(struct net_device *dev, struct sk_buff *skb,
> -                            void *accel_priv, select_queue_fallback_t
> fallback)
> -{
> -     unsigned int num_queues = dev->real_num_tx_queues;
> -     u32 hash;
> -     u16 queue_index;
> -
> -     /* First, check if there is only one queue to optimise the
> -      * single-queue or old frontend scenario.
> -      */
> -     if (num_queues == 1) {
> -             queue_index = 0;
> -     } else {
> -             /* Use skb_get_hash to obtain an L4 hash if available */
> -             hash = skb_get_hash(skb);
> -             queue_index = hash % num_queues;
> -     }
> -
> -     return queue_index;
> -}
> -
>  static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>       struct xenvif *vif = netdev_priv(dev);
>       struct xenvif_queue *queue = NULL;
> -     unsigned int num_queues = dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       u16 index;
>       int min_slots_needed;
> 
> @@ -225,7 +204,7 @@ 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 = dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       unsigned long rx_bytes = 0;
>       unsigned long rx_packets = 0;
>       unsigned long tx_bytes = 0;
> @@ -256,7 +235,7 @@ out:
>  static void xenvif_up(struct xenvif *vif)
>  {
>       struct xenvif_queue *queue = NULL;
> -     unsigned int num_queues = vif->dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       unsigned int queue_index;
> 
>       for (queue_index = 0; queue_index < num_queues;
> ++queue_index) {
> @@ -272,7 +251,7 @@ static void xenvif_up(struct xenvif *vif)
>  static void xenvif_down(struct xenvif *vif)
>  {
>       struct xenvif_queue *queue = NULL;
> -     unsigned int num_queues = vif->dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       unsigned int queue_index;
> 
>       for (queue_index = 0; queue_index < num_queues;
> ++queue_index) {
> @@ -379,7 +358,7 @@ static void xenvif_get_ethtool_stats(struct
> net_device *dev,
>                                    struct ethtool_stats *stats, u64 * data)
>  {
>       struct xenvif *vif = netdev_priv(dev);
> -     unsigned int num_queues = dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       int i;
>       unsigned int queue_index;
>       struct xenvif_stats *vif_stats;
> @@ -424,7 +403,6 @@ static const struct net_device_ops
> xenvif_netdev_ops = {
>       .ndo_fix_features = xenvif_fix_features,
>       .ndo_set_mac_address = eth_mac_addr,
>       .ndo_validate_addr   = eth_validate_addr,
> -     .ndo_select_queue = xenvif_select_queue,

Ok, so we are in a situation where the frontend does not know what the backend 
is doing. I guess, since the negotiation of the algorithm through xenstore is 
completely lacking at the moment, then this is the status quo. So using the 
default __netdev_pick_tx() is ok.
I do think the fact that the frontend doesn't care what algorithm the backend 
is using needs to be made explicit though. I'll see what I can do this week.

  Paul

>  };
> 
>  struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
> @@ -438,7 +416,7 @@ struct xenvif *xenvif_alloc(struct device *parent,
> domid_t domid,
>       snprintf(name, IFNAMSIZ - 1, "vif%u.%u", domid, handle);
>       /* Allocate a netdev with the max. supported number of queues.
>        * When the guest selects the desired number, it will be updated
> -      * via netif_set_real_num_tx_queues().
> +      * via netif_set_real_num_*_queues().
>        */
>       dev = alloc_netdev_mq(sizeof(struct xenvif), name, ether_setup,
>                             xenvif_max_queues);
> @@ -458,11 +436,9 @@ struct xenvif *xenvif_alloc(struct device *parent,
> domid_t domid,
>       vif->dev = dev;
>       vif->disabled = false;
> 
> -     /* Start out with no queues. The call below does not require
> -      * rtnl_lock() as it happens before register_netdev().
> -      */
> +     /* Start out with no queues. */
>       vif->queues = NULL;
> -     netif_set_real_num_tx_queues(dev, 0);
> +     vif->num_queues = 0;
> 
>       dev->netdev_ops = &xenvif_netdev_ops;
>       dev->hw_features = NETIF_F_SG |
> @@ -677,7 +653,7 @@ static void xenvif_wait_unmap_timeout(struct
> xenvif_queue *queue,
>  void xenvif_disconnect(struct xenvif *vif)
>  {
>       struct xenvif_queue *queue = NULL;
> -     unsigned int num_queues = vif->dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       unsigned int queue_index;
> 
>       if (netif_carrier_ok(vif->dev))
> @@ -724,7 +700,7 @@ void xenvif_deinit_queue(struct xenvif_queue
> *queue)
>  void xenvif_free(struct xenvif *vif)
>  {
>       struct xenvif_queue *queue = NULL;
> -     unsigned int num_queues = vif->dev->real_num_tx_queues;
> +     unsigned int num_queues = vif->num_queues;
>       unsigned int queue_index;
>       /* Here we want to avoid timeout messages if an skb can be
> legitimately
>        * stuck somewhere else. Realistically this could be an another vif's
> @@ -748,12 +724,9 @@ void xenvif_free(struct xenvif *vif)
>               xenvif_deinit_queue(queue);
>       }
> 
> -     /* Free the array of queues. The call below does not require
> -      * rtnl_lock() because it happens after unregister_netdev().
> -      */
> -     netif_set_real_num_tx_queues(vif->dev, 0);
>       vfree(vif->queues);
>       vif->queues = NULL;
> +     vif->num_queues = 0;
> 
>       free_netdev(vif->dev);
> 
> diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-
> netback/xenbus.c
> index 96c63dc2..3d85acd 100644
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -527,9 +527,7 @@ static void connect(struct backend_info *be)
>       /* Use the number of queues requested by the frontend */
>       be->vif->queues = vzalloc(requested_num_queues *
>                                 sizeof(struct xenvif_queue));
> -     rtnl_lock();
> -     netif_set_real_num_tx_queues(be->vif->dev,
> requested_num_queues);
> -     rtnl_unlock();
> +     be->vif->num_queues = requested_num_queues;
> 
>       for (queue_index = 0; queue_index < requested_num_queues;
> ++queue_index) {
>               queue = &be->vif->queues[queue_index];
> @@ -546,9 +544,7 @@ static void connect(struct backend_info *be)
>                        * earlier queues can be destroyed using the regular
>                        * disconnect logic.
>                        */
> -                     rtnl_lock();
> -                     netif_set_real_num_tx_queues(be->vif->dev,
> queue_index);
> -                     rtnl_unlock();
> +                     be->vif->num_queues = queue_index;
>                       goto err;
>               }
> 
> @@ -561,13 +557,19 @@ static void connect(struct backend_info *be)
>                        * and also clean up any previously initialised queues.
>                        */
>                       xenvif_deinit_queue(queue);
> -                     rtnl_lock();
> -                     netif_set_real_num_tx_queues(be->vif->dev,
> queue_index);
> -                     rtnl_unlock();
> +                     be->vif->num_queues = queue_index;
>                       goto err;
>               }
>       }
> 
> +     /* Initialisation completed, tell core driver the number of
> +      * active queues.
> +      */
> +     rtnl_lock();
> +     netif_set_real_num_tx_queues(be->vif->dev,
> requested_num_queues);
> +     netif_set_real_num_rx_queues(be->vif->dev,
> requested_num_queues);
> +     rtnl_unlock();
> +
>       xenvif_carrier_on(be->vif);
> 
>       unregister_hotplug_status_watch(be);
> @@ -582,13 +584,11 @@ static void connect(struct backend_info *be)
>       return;
> 
>  err:
> -     if (be->vif->dev->real_num_tx_queues > 0)
> +     if (be->vif->num_queues > 0)
>               xenvif_disconnect(be->vif); /* Clean up existing queues */
>       vfree(be->vif->queues);
>       be->vif->queues = NULL;
> -     rtnl_lock();
> -     netif_set_real_num_tx_queues(be->vif->dev, 0);
> -     rtnl_unlock();
> +     be->vif->num_queues = 0;
>       return;
>  }
> 
> @@ -596,7 +596,7 @@ err:
>  static int connect_rings(struct backend_info *be, struct xenvif_queue
> *queue)
>  {
>       struct xenbus_device *dev = be->dev;
> -     unsigned int num_queues = queue->vif->dev-
> >real_num_tx_queues;
> +     unsigned int num_queues = queue->vif->num_queues;
>       unsigned long tx_ring_ref, rx_ring_ref;
>       unsigned int tx_evtchn, rx_evtchn;
>       int err;
> --
> 1.7.10.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel