From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCHv3 2/6] evtchn: defer freeing struct evtchn's until evtchn_destroy_final() Date: Fri, 19 Jun 2015 11:55:57 +0100 Message-ID: <5584115D0200007800086FC4@mail.emea.novell.com> References: <1434542583-28073-1-git-send-email-david.vrabel@citrix.com> <1434542583-28073-3-git-send-email-david.vrabel@citrix.com> <5582BB4C02000078000868FB@mail.emea.novell.com> <5582A02A.9050803@citrix.com> <5583FD0F0200007800086EF1@mail.emea.novell.com> <5583E655.2070807@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Z5txm-0003sO-5G for xen-devel@lists.xenproject.org; Fri, 19 Jun 2015 10:55:58 +0000 In-Reply-To: <5583E655.2070807@citrix.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel Cc: xen-devel@lists.xenproject.org, Keir Fraser , Ian Campbell , Tim Deegan List-Id: xen-devel@lists.xenproject.org >>> On 19.06.15 at 11:52, wrote: > On 19/06/15 10:29, Jan Beulich wrote: >>>>> On 18.06.15 at 12:40, wrote: >>> On 18/06/15 11:36, Jan Beulich wrote: >>>>>>> On 17.06.15 at 14:02, 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. Jan