Re: [Qemu-devel] [PATCH v2 2/6] net: introduce lock to protect NetClientState's peer's access

[liu ping fan]

On Tue, Jun 18, 2013 at 8:25 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Thu, Jun 13, 2013 at 05:03:02PM +0800, Liu Ping Fan wrote:
>> @@ -67,6 +67,10 @@ struct NetClientState {
>>      NetClientInfo *info;
>>      int link_down;
>>      QTAILQ_ENTRY(NetClientState) next;
>> +    /* protect the race access of peer only between reader and writer.
>> +         * to resolve the writer's race condition, resort on biglock.
>> +         */
>
> Indentation
>
Will fix.
>> @@ -301,6 +303,38 @@ static void qemu_free_net_client(NetClientState *nc)
>>      }
>>  }
>>
>> +/* elimate the reference and sync with exit of rx/tx action.
>
> s/elimate/Eliminate/
>
Will fix
>> + * And flush out peer's queue.
>> + */
>> +static void qemu_net_client_detach_flush(NetClientState *nc)
>> +{
>> +    NetClientState *peer;
>> +
>> +    /* reader of self's peer field , fixme? the deleters are not concurrent,
>> +         * so this pair lock can save.
>> +         */
>
> Indentation, also please resolve the fixme.
>
So, here can I take the assumption that the deleters are serialized by
biglock, and remove the lock following this comment?

>> @@ -394,6 +433,28 @@ int qemu_can_send_packet(NetClientState *sender)
>>      return 1;
>>  }
>>
>> +int qemu_can_send_packet(NetClientState *sender)
>> +{
>> +    int ret = 1;
>> +
>> +    qemu_mutex_lock(&sender->peer_lock);
>> +    if (!sender->peer) {
>> +        goto unlock;
>> +    }
>> +
>> +    if (sender->peer->receive_disabled) {
>> +        ret = 0;
>> +        goto unlock;
>> +    } else if (sender->peer->info->can_receive &&
>> +               !sender->peer->info->can_receive(sender->peer)) {
>> +        ret = 0;
>> +        goto unlock;
>> +    }
>
> Just call qemu_can_send_packet_nolock() instead of duplicating code?

Yes.

Thx & regards,
pingfan