Re: [Xen-devel] [PATCHv2 2/5] evtchn: simplify port_is_valid()

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-06-15 at 16:59 +0100, David Vrabel wrote:
> On 15/06/15 16:57, Ian Campbell wrote:
> > On Mon, 2015-06-15 at 16:48 +0100, David Vrabel wrote:
> >> By keeping a count of the number of currently valid event channels,
> >> port_is_valid() can be simplified.
> >>
> >> d->valid_evtchns can also be tested without holding d->event_lock which
> >> will be useful later on.
> >>
> >> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> >> ---
> >> v2:
> >> - Used unsigned int for d->valid_evtchns.
> >> ---
> >>  xen/common/event_channel.c |    3 +++
> >>  xen/include/xen/event.h    |    4 +---
> >>  xen/include/xen/sched.h    |    5 +++--
> >>  3 files changed, 7 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
> >> index 947880f..fd48646 100644
> >> --- a/xen/common/event_channel.c
> >> +++ b/xen/common/event_channel.c
> >> @@ -189,6 +189,8 @@ static int get_free_port(struct domain *d)
> >>          return -ENOMEM;
> >>      bucket_from_port(d, port) = chn;
> >>  
> >> +    write_atomic(&d->valid_evtchns, d->valid_evtchns + 
> >> EVTCHNS_PER_BUCKET);
> > 
> > Shouldn't this be atomic_add? Otherwise the result of what you have here
> > is actually a non-atomic read/add/write.
> 
> This field is only updated while holding d->event_lock.  Only reads are
> unlocked.

Oh good, thanks!

Ian.


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