Re: [Xen-devel] [PATCHv3 5/6] evtchn: remove the locking when unmasking an event channel

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 18/06/15 12:30, Jan Beulich wrote:
>>>> On 17.06.15 at 14:03, <david.vrabel@xxxxxxxxxx> wrote:
>> --- a/xen/common/event_channel.c
>> +++ b/xen/common/event_channel.c
>> @@ -978,8 +978,6 @@ int evtchn_unmask(unsigned int port)
>>      struct domain *d = current->domain;
>>      struct evtchn *evtchn;
>>  
>> -    ASSERT(spin_is_locked(&d->event_lock));
>> -
>>      if ( unlikely(!port_is_valid(d, port)) )
>>          return -EINVAL;
>>  
>> @@ -1146,9 +1144,7 @@ long do_event_channel_op(int cmd, 
>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>          struct evtchn_unmask unmask;
>>          if ( copy_from_guest(&unmask, arg, 1) != 0 )
>>              return -EFAULT;
>> -        spin_lock(&current->domain->event_lock);
>>          rc = evtchn_unmask(unmask.port);
>> -        spin_unlock(&current->domain->event_lock);
> 
> And, looking particularly at evtchn_fifo_unmask() (and its descendant
> evtchn_fifo_set_pending()), you get away without acquiring the port
> lock in or around evtchn_port_unmask()? If indeed so, this one would
> again be independent on 1, 2, and 4, i.e. could go in together with 3.

Yes.  This is only dependent on #3 (simplify port_is_valid()).

David

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