From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCHv2 3/5] evtchn: use a per-event channel lock
 for sending events
Date: Tue, 16 Jun 2015 10:34:43 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, Tim Deegan <tim@xen.org>
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On 16/06/15 10:18, Jan Beulich wrote:
>>>> On 15.06.15 at 17:48, <david.vrabel@citrix.com> 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