Re: [ANNOUNCE] Xen 4.15 - call for notification/status of significant bugs

From: Tamas K Lengyel <tamas.k.lengyel@gmail.com>
To: Dario Faggioli <dfaggioli@suse.com>
Cc: Ian Jackson <iwj@xenproject.org>,
	Committers <committers@xenproject.org>,
	 Xen-devel <xen-devel@lists.xenproject.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	 Jan Beulich <jbeulich@suse.com>, Julien Grall <julien@xen.org>,
	community.manager@xenproject.org
Subject: Re: [ANNOUNCE] Xen 4.15 - call for notification/status of significant bugs
Date: Thu, 4 Feb 2021 10:00:55 -0500	[thread overview]
Message-ID: <CABfawhkT5JBsT2-reSLB-bNFhP1em5U3vBs+z_FM6_Kcd7TSiQ@mail.gmail.com> (raw)
In-Reply-To: <6d0d7181bad79259aff28351621d2ac1eeaca113.camel@suse.com>

On Thu, Feb 4, 2021 at 9:21 AM Dario Faggioli <dfaggioli@suse.com> wrote:
>
> On Thu, 2021-02-04 at 12:12 +0000, Ian Jackson wrote:
> > B. "scheduler broken" bugs.
> >
> > Information from
> >   Andrew Cooper <andrew.cooper3@citrix.com>
> >   Dario Faggioli <dfaggioli@suse.com>
> >
> > Quoting Andrew Cooper
> > > We've had 4 or 5 reports of Xen not working, and very little
> > > investigation on whats going on.  Suspicion is that there might be
> > > two bugs, one with smt=0 on recent AMD hardware, and one more
> > > general "some workloads cause negative credit" and might or might
> > > not be specific to credit2 (debugging feedback differs - also might
> > > be 3 underlying issue).
> >
> > I reviewed a thread about this and it is not clear to me where we are
> > with this.
> >
> Ok, let me try to summarize the current status.
>
> - BUG: credit=sched2 machine hang when using DRAKVUF
>
>   https://lists.xen.org/archives/html/xen-devel/2020-05/msg01985.html
>   https://lists.xenproject.org/archives/html/xen-devel/2020-10/msg01561.html
>   https://bugzilla.opensuse.org/show_bug.cgi?id=1179246
>
>   99% sure that it's a Credit2 scheduler issue.
>   I'm actively working on it.
>   "Seems a tricky one; I'm still in the analysis phase"
>
>   Manifests only with certain combination of hardware and workload.
>   I'm not reproducing, but there are multiple reports of it (see
>   above). I'm investigating and trying to come up at least with
>   debug patches that one of the reporter should be able and willing to
>   test.
>
> - Null scheduler and vwfi native problem
>
>   https://lists.xenproject.org/archives/html/xen-devel/2021-01/msg01634.html
>
>   RCU issues, but manifests due to scheduler behavior (especially
>   NULL scheduler, especially on ARM).
>   I'm actively working on it.
>
>   Patches that should solve the issue for ARM posted already. They
>   will need to be slightly adjusted to cover x86 as well. Waiting a
>   couple days more for a confirmation from the reporter that the
>   patches do help, at least on ARM.
>

I've run into null-scheduler causing CPU lockups as well on x86.
Required physical machine reboot. Seems to be triggered with domain
destruction when destroying fork vms. Happens only intermittently.

Tamas