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



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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