Re: [Xen-devel] [PATCH 00/60] xen: add core scheduling support

[Juergen Gross <jgross@xxxxxxxx>]

On 19.07.19 07:41, Juergen Gross wrote:
> On 18.07.19 17:14, Sergey Dyasli wrote:
> > On 18/07/2019 15:48, Juergen Gross wrote:
> > > On 15.07.19 16:08, Sergey Dyasli wrote:
> > > > On 05/07/2019 14:56, Dario Faggioli wrote:
> > > > > On Fri, 2019-07-05 at 14:17 +0100, Sergey Dyasli wrote:
> > > > > > 1) This crash is quite likely to happen:
> > > > > >
> > > > > > [2019-07-04 18:22:46 UTC] (XEN) [ 3425.220660] Watchdog timer detects
> > > > > > that CPU2 is stuck!
> > > > > > [2019-07-04 18:22:46 UTC] (XEN) [ 3425.226293] ----[ Xen-4.13.0-
> > > > > > 8.0.6-d  x86_64  debug=y   Not tainted ]----
> > > > > > [...]
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [ 3425.501989] Xen call trace:
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.505278]    [<ffff82d08023d578>] vcpu_sleep_sync+0x50/0x71
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.511518]    [<ffff82d080208370>] vcpu_pause+0x21/0x23
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.517326]    [<ffff82d08023e25d>]
> > > > > > vcpu_set_periodic_timer+0x27/0x73
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.524258]    [<ffff82d080209682>] do_vcpu_op+0x2c9/0x668
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.530238]    [<ffff82d08024f970>] compat_vcpu_op+0x250/0x390
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.536566]    [<ffff82d080383964>] pv_hypercall+0x364/0x564
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.542719]    [<ffff82d080385644>] do_entry_int82+0x26/0x2d
> > > > > > [2019-07-04 18:22:47 UTC] (XEN) [
> > > > > > 3425.548876]    [<ffff82d08038839b>] entry_int82+0xbb/0xc0
> > > > > Mmm... vcpu_set_periodic_timer?
> > > > >
> > > > > What kernel is this and when does this crash happen?
> > > > Hi Dario,
> > > >
> > > > I can easily reproduce this crash using a Debian 7 PV VM (2 vCPUs, 
> > > > 2GB RAM)
> > > > which has the following kernel:
> > > >
> > > > # uname -a
> > > >
> > > > Linux localhost 3.2.0-4-amd64 #1 SMP Debian 3.2.78-1 x86_64 GNU/Linux
> > > >
> > > > All I need to do is suspend and resume the VM.
> > > Happens with a more recent kernel, too.
> > >
> > > I can easily reproduce the issue with any PV guest with more than 1 vcpu
> > > by doing "xl save" and then "xl restore" again.
> > >
> > > With the reproducer being available I'm now diving into the issue...
> > One further thing to add is that I was able to avoid the crash by 
> > reverting
> >     xen/sched: rework and rename vcpu_force_reschedule()
> >
> > which is a part of the series. This made all tests with PV guests pass.
> Yeah, but removing this patch is just papering over a general issue.
> The main problem seems to be a vcpu trying to pause another vcpu of the
> same sched_unit. I already have an idea what is really happening, I just
> need to verify it.
Was another problem as I thought initially, but I've found it.

xl restore is working now. :-)


Juergen

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