On 05/23/2013 07:41 PM, Michael S. Tsirkin wrote:
> On Thu, May 23, 2013 at 11:12:30AM +0800, Jason Wang wrote:
>> Linear search were used in both get_slot() and macvtap_get_queue(), this is
>> because:
>>
>> - macvtap didn't reshuffle the array of taps when create or destroy a queue, 
>> so
>>   when adding a new queue, macvtap must do linear search to find a location 
>> for
>>   the new queue. This will also complicate the TUNSETQUEUE implementation for
>>   multiqueue API.
>> - the queue itself didn't track the queue index, so the we must do a linear
>>   search in the array to find the location of a existed queue.
>>
>> The solution is straightforward: reshuffle the array and introduce a 
>> queue_index
>> to macvtap_queue.
>>
>> Signed-off-by: Jason Wang <jasow...@redhat.com>
>> ---
>>  drivers/net/macvtap.c |   63 
>> +++++++++++++++---------------------------------
>>  1 files changed, 20 insertions(+), 43 deletions(-)
>>
>> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
>> index a36e49e..5fd341c 100644
>> --- a/drivers/net/macvtap.c
>> +++ b/drivers/net/macvtap.c
>> @@ -44,6 +44,7 @@ struct macvtap_queue {
>>      struct macvlan_dev __rcu *vlan;
>>      struct file *file;
>>      unsigned int flags;
>> +    u16 queue_index;
>>  };
>>  
>>  static struct proto macvtap_proto = {
>> @@ -84,30 +85,10 @@ static const struct proto_ops macvtap_socket_ops;
>>   */
>>  static DEFINE_SPINLOCK(macvtap_lock);
>>  
>> -/*
>> - * get_slot: return a [unused/occupied] slot in vlan->taps[]:
>> - *  - if 'q' is NULL, return the first empty slot;
>> - *  - otherwise, return the slot this pointer occupies.
>> - */
>> -static int get_slot(struct macvlan_dev *vlan, struct macvtap_queue *q)
>> -{
>> -    int i;
>> -
>> -    for (i = 0; i < MAX_MACVTAP_QUEUES; i++) {
>> -            if (rcu_dereference_protected(vlan->taps[i],
>> -                                          lockdep_is_held(&macvtap_lock)) 
>> == q)
>> -                    return i;
>> -    }
>> -
>> -    /* Should never happen */
>> -    BUG_ON(1);
>> -}
>> -
>>  static int macvtap_set_queue(struct net_device *dev, struct file *file,
>>                              struct macvtap_queue *q)
>>  {
>>      struct macvlan_dev *vlan = netdev_priv(dev);
>> -    int index;
>>      int err = -EBUSY;
>>  
>>      spin_lock(&macvtap_lock);
>> @@ -115,12 +96,12 @@ static int macvtap_set_queue(struct net_device *dev, 
>> struct file *file,
>>              goto out;
>>  
>>      err = 0;
>> -    index = get_slot(vlan, NULL);
>>      rcu_assign_pointer(q->vlan, vlan);
>> -    rcu_assign_pointer(vlan->taps[index], q);
>> +    rcu_assign_pointer(vlan->taps[vlan->numvtaps], q);
>>      sock_hold(&q->sk);
>>  
>>      q->file = file;
>> +    q->queue_index = vlan->numvtaps;
>>      file->private_data = q;
>>  
>>      vlan->numvtaps++;
>> @@ -140,16 +121,23 @@ out:
>>   */
>>  static void macvtap_put_queue(struct macvtap_queue *q)
>>  {
>> +    struct macvtap_queue *nq;
>>      struct macvlan_dev *vlan;
>>  
>>      spin_lock(&macvtap_lock);
>>      vlan = rcu_dereference_protected(q->vlan,
>>                                       lockdep_is_held(&macvtap_lock));
>>      if (vlan) {
>> -            int index = get_slot(vlan, q);
>> +            int index = q->queue_index;
>> +            BUG_ON(index >= vlan->numvtaps);
>>  
>> -            RCU_INIT_POINTER(vlan->taps[index], NULL);
>> +            rcu_assign_pointer(vlan->taps[index],
>> +                               vlan->taps[vlan->numvtaps - 1]);
>>              RCU_INIT_POINTER(q->vlan, NULL);
>> +            nq = rcu_dereference_protected(vlan->taps[index],
>> +                                           lockdep_is_held(&macvtap_lock));
>> +            nq->queue_index = index;
>> +
>>              sock_put(&q->sk);
> Hmm this looks like a bug BTW: sock_put should be after
> no one uses this tap, so must be after synchronize_rcu.
> No?

Two refcnts were held, one is the socket itself (and we can safely put
it here), another is held by device when doing macvtap_set_queue(), it
was released by another sock_put() after synchronize_rcu().
>
>>              --vlan->numvtaps;
>>      }
> So:
>               nq = rcu_dereference_protected(vlan->taps[vlan->numvtaps - 1],
>                                              lockdep_is_held(&macvtap_lock));
>               rcu_assign_pointer(vlan->taps[index], nq);
>
> same thing?

Same and cleaner, thanks.
>
>> @@ -182,8 +170,7 @@ static struct macvtap_queue *macvtap_get_queue(struct 
>> net_device *dev,
>>      rxq = skb_get_rxhash(skb);
>>      if (rxq) {
>>              tap = rcu_dereference(vlan->taps[rxq % numvtaps]);
>> -            if (tap)
>> -                    goto out;
>> +            goto out;
>>      }
>>  
>>      if (likely(skb_rx_queue_recorded(skb))) {
>> @@ -193,17 +180,10 @@ static struct macvtap_queue *macvtap_get_queue(struct 
>> net_device *dev,
>>                      rxq -= numvtaps;
>>  
>>              tap = rcu_dereference(vlan->taps[rxq]);
>> -            if (tap)
>> -                    goto out;
>> -    }
>> -
>> -    /* Everything failed - find first available queue */
>> -    for (rxq = 0; rxq < MAX_MACVTAP_QUEUES; rxq++) {
>> -            tap = rcu_dereference(vlan->taps[rxq]);
>> -            if (tap)
>> -                    break;
>> +            goto out;
>>      }
>>  
>> +    tap = rcu_dereference(vlan->taps[0]);
>>  out:
>>      return tap;
>>  }
>> @@ -221,17 +201,14 @@ static void macvtap_del_queues(struct net_device *dev)
>>  
>>      /* macvtap_put_queue can free some slots, so go through all slots */
>>      spin_lock(&macvtap_lock);
>> -    for (i = 0; i < MAX_MACVTAP_QUEUES && vlan->numvtaps; i++) {
>> +    for (i = 0; i < vlan->numvtaps; i++) {
>>              q = rcu_dereference_protected(vlan->taps[i],
>>                                            lockdep_is_held(&macvtap_lock));
>> -            if (q) {
>> -                    qlist[j++] = q;
>> -                    RCU_INIT_POINTER(vlan->taps[i], NULL);
>> -                    RCU_INIT_POINTER(q->vlan, NULL);
>> -                    vlan->numvtaps--;
>> -            }
>> +            BUG_ON(q == NULL);
>> +            qlist[j++] = q;
>> +            RCU_INIT_POINTER(vlan->taps[i], NULL);
>> +            RCU_INIT_POINTER(q->vlan, NULL);
>>      }
>> -    BUG_ON(vlan->numvtaps != 0);
>>      /* guarantee that any future macvtap_set_queue will fail */
>>      vlan->numvtaps = MAX_MACVTAP_QUEUES;
>>      spin_unlock(&macvtap_lock);
>> -- 
>> 1.7.1

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