Re: [Xen-devel] PV-shim 4.13 assertion failures during vcpu_wake()

[Jürgen Groß <jgross@xxxxxxxx>]

On 21.10.19 13:36, Roger Pau Monné wrote:
> On Mon, Oct 21, 2019 at 12:52:10PM +0200, Jürgen Groß wrote:
> > On 21.10.19 11:51, Sergey Dyasli wrote:
> > > Hello,
> > >
> > > While testing pv-shim from a snapshot of staging 4.13 branch (with core-
> > > scheduling patches applied), some sort of scheduling issues were uncovered
> > > which usually leads to a guest lockup (sometimes with soft lockup messages
> > > from Linux kernel).
> > >
> > > This happens more frequently on SandyBridge CPUs. After enabling
> > > CONFIG_DEBUG in pv-shim, the following assertions failed:
> > >
> > > Null scheduler:
> > >
> > >       Assertion 'lock == get_sched_res(i->res->master_cpu)->schedule_lock' 
> > > failed at ...are/xen-dir/xen-root/xen/include/xen/sched-if.h:278
> > >       (full crash log: https://paste.debian.net/1108861/ )
> > >
> > > Credit1 scheduler:
> > >
> > >       Assertion 'cpumask_cycle(cpu, unit->cpu_hard_affinity) == cpu' failed at 
> > > sched_credit.c:383
> > >       (full crash log: https://paste.debian.net/1108862/ )
> > >
> > > I'm currently investigation those, but would appreciate any help or
> > > suggestions.
> > Hmm, I think that pv_shim_cpu_up() shouldn't do the vcpu_wake(), but the
> > caller.
> >
> > Does the attached patch help?
> >
> >
> > Juergen
> >  From 068ea0419d1a67e967b9431ed11e24b731cd357f Mon Sep 17 00:00:00 2001
> > From: Juergen Gross <jgross@xxxxxxxx>
> > Date: Mon, 21 Oct 2019 12:28:33 +0200
> > Subject: [PATCH] xen/shim: fix pv-shim cpu up/down
> >
> > Calling vcpu_wake() from pv_shim_cpu_up() is wrong as it is not yet
> > sure that the correct scheduler has taken over the cpu.
> I'm not sure why this is wrong, the scheduler should be capable of
> handling 2 vCPUs on a single pCPU while the new pCPU is brought
> online?
Oh, right, I made some false assumptions.

This patch is pure nonsense.


Juergen

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