From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [GIT PULL] Fix lost interrupt race in Xen event channels Date: Mon, 30 Aug 2010 10:22:24 +0100 Message-ID: <4C7B94700200007800012C74@vpn.id2.novell.com> References: <4C7B909F0200007800012C52@vpn.id2.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: Jeremy Fitzhardinge , "Xen-devel@lists.xensource.com" , Tom Kopec , Daniel Stodden List-Id: xen-devel@lists.xenproject.org >>> On 30.08.10 at 11:15, Keir Fraser wrote: > On 30/08/2010 10:06, "Jan Beulich" wrote: >=20 >> However, do you also think that pirq_unmask_and_notify() is safe >> to be called twice? I would think the double EOI potentially sent to >> Xen could lead to an interrupt getting ack-ed that didn't even get >> started to be serviced yet. >=20 > Erm, well if this is a race that happens only occasionally, does it = matter? > Worst case you get another interrupt straight away. Only a problem if it > happens often enough to cause a performance issue or even livelock = interrupt > storm. I wasn't worried about the level case, but rather the edge one. I forgot, however, that edge ones are ACKTYPE_NONE in Xen, so indeed there shouldn't be a problem unless IRQs get moved around at a very high rate (which clearly they shouldn't). Jan