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:
>> @@ -609,21 +662,18 @@ int evtchn_send(struct domain *ld, unsigned int lport)
>>      struct domain *rd;
>>      int            rport, ret = 0;
>>  
>> -    spin_lock(&ld->event_lock);
>> -
>> -    if ( unlikely(!port_is_valid(ld, lport)) )
>> -    {
>> -        spin_unlock(&ld->event_lock);
>> +    if ( unlikely(lport >= read_atomic(&ld->valid_evtchns)) )
>>          return -EINVAL;
>> -    }
> 
> I don't think you really want to open code part of port_is_valid()
> (and avoid other parts of it) here? Or if really so, I think a comment
> should be added to explain it.

The ld->valid_evtchns is the only field we can safely check without
ld->event_lock.

We do check the channel state and the code that set this state uses the
full port_is_valid() call.  I'll add a comment.

> And then - no change to free_xen_event_channel()?

It looked alright to me, but now I see the clear of xen_consumer needs
to be done under the channel lock.  Probably by moving it to
__evtchn_close().

David



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