From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <ian.campbell@citrix.com>
Subject: Re: [PATCHv2 2/5] evtchn: simplify port_is_valid()
Date: Mon, 15 Jun 2015 16:57:46 +0100
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To: David Vrabel <david.vrabel@citrix.com>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>, Tim Deegan <tim@xen.org>, Jan Beulich <jbeulich@suse.com>
List-Id: xen-devel@lists.xenproject.org

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@citrix.com>
> ---
> 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.

Ian.