On 19/06/15 11:55, Jan Beulich wrote:
>>>> On 19.06.15 at 11:52, <david.vra...@citrix.com> wrote:
>> On 19/06/15 10:29, Jan Beulich wrote:
>>>>>> On 18.06.15 at 12:40, <david.vra...@citrix.com> wrote:
>>>> On 18/06/15 11:36, Jan Beulich wrote:
>>>>>>>> On 17.06.15 at 14:02, <david.vra...@citrix.com> wrote:
>>>>>> --- a/xen/common/event_channel.c
>>>>>> +++ b/xen/common/event_channel.c
>>>>>> @@ -1175,22 +1175,6 @@ int alloc_unbound_xen_event_channel(
>>>>>>
>>>>>> void free_xen_event_channel(struct domain *d, int port)
>>>>>> {
>>>>>> - struct evtchn *chn;
>>>>>> -
>>>>>> - spin_lock(&d->event_lock);
>>>>>> -
>>>>>> - if ( unlikely(d->is_dying) )
>>>>>> - {
>>>>>> - spin_unlock(&d->event_lock);
>>>>>> - return;
>>>>>> - }
>>>>>> -
>>>>>> - BUG_ON(!port_is_valid(d, port));
>>>>
>>>> I can keep this one.
>>>>
>>>>>> - chn = evtchn_from_port(d, port);
>>>>>> - BUG_ON(!consumer_is_xen(chn));
>>>>>
>>>>> At least in debug builds I think these would better be retained.
>>>>
>>>> But this one has to go because it will always trip when
>>>> free_xen_event_channel() is called after evtchn_destroy() (which will
>>>> have cleared xen_consumer).
>>>
>>> Then why not
>>>
>>> BUG_ON(!consumer_is_xen(chn) && !d->is_dying);
>>>
>>> or keep the d->is_dying check in place? I can see why accelerating
>>> notify_via_xen_event_channel() is useful, but
>>> free_xen_event_channel()?
>>
>> This BUG_ON() is a pretty weak check and I don't really see the point of
>> it. I'm not respinning v4 just for this.
>
> I'm not sure what makes this more weak than the other BUG_ON()
> you agreed to retain - both try to validate that the callers don't do
> bad things. Admitted, both would better be ASSERT()s...
>
> As to spinning v4 - I see no need, as I can easily adjust this while
> committing, as long as you don't disagree to have your name under
> the result.
I disagree.
For this assert to be safe it needs to take suitable locks such as:
#ifdef DEBUG
struct evtchn *chn;
chn = evtchn_from_port(d, port);
spin_lock(&chn->lock);
BUG_ON(chn->state != ECS_FREE && !consumer_is_xen(chn));
spin_unlock(&chn->lock);
#endif
or if you want the is_dying check, you need the event lock instead.
I wrote the first one, saw it was lots of noise for almost no gain and
threw it away.
David
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