Re: [Xen-devel] [PATCHv2 3/5] evtchn: use a per-event channel lock for sending events

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 16/06/15 10:18, Jan Beulich wrote:
>>>> On 15.06.15 at 17:48, <david.vrabel@xxxxxxxxxx> wrote:
>> @@ -1163,11 +1213,15 @@ int alloc_unbound_xen_event_channel(
>>      if ( rc )
>>          goto out;
>>  
>> +    spin_lock(&chn->lock);
>> +
>>      chn->state = ECS_UNBOUND;
>>      chn->xen_consumer = get_xen_consumer(notification_fn);
>>      chn->notify_vcpu_id = lvcpu;
>>      chn->u.unbound.remote_domid = remote_domid;
>>  
>> +    spin_unlock(&chn->lock);
>> +
>>   out:
>>      spin_unlock(&ld->event_lock);
> 
> I don't see why you shouldn't be able to move up this unlock.

Because we need to (also) hold ld->event_lock while changing the state
from ECS_FREE or a concurrent get_free_port() will find this port again.

>> @@ -1221,6 +1277,8 @@ void notify_via_xen_event_channel(struct domain *ld, 
>> int lport)
>>          evtchn_port_set_pending(rd, rchn->notify_vcpu_id, rchn);
>>      }
>>  
>> +    spin_unlock(&lchn->lock);
>> +
>>      spin_unlock(&ld->event_lock);
>>  }
> 
> Again I think the event lock can be dropped earlier now.

Ditto.

David

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