Re: [PATCH 04/12] evtchn: evtchn_set_priority() needs to acquire the per-channel lock

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.09.2020 12:21, Julien Grall wrote:
> On 28/09/2020 11:57, Jan Beulich wrote:
>> evtchn_fifo_set_pending() (invoked with the per-channel lock held) has
>> two uses of the channel's priority field. The field gets updated by
>> evtchn_fifo_set_priority() with only the per-domain event_lock held,
>> i.e. the two reads may observe two different values. While the 2nd use
>> could - afaict - in principle be replaced by q->priority, I think
>> evtchn_set_priority() should acquire the per-channel lock in any event.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/common/event_channel.c
>> +++ b/xen/common/event_channel.c
>> @@ -1132,7 +1132,9 @@ static long evtchn_set_priority(const st
>>   {
>>       struct domain *d = current->domain;
>>       unsigned int port = set_priority->port;
>> +    struct evtchn *chn;
>>       long ret;
>> +    unsigned long flags;
>>   
>>       spin_lock(&d->event_lock);
> 
> Is it still necessary to hold d->event_lock?

Good point - I see no reason for it to be held anymore.

Jan