Re: Crash when using cpupools

[Juergen Gross <jgross@xxxxxxxx>]

On 06.09.21 11:28, Juergen Gross wrote:
> On 06.09.21 10:46, Andrew Cooper wrote:
> > On 06/09/2021 09:23, Juergen Gross wrote:
> > > On 03.09.21 17:41, Bertrand Marquis wrote:
> > > > Hi,
> > > >
> > > > While doing some investigation with cpupools I encountered a crash
> > > > when trying to isolate a guest to its own physical cpu.
> > > >
> > > > I am using current staging status.
> > > >
> > > > I did the following (on FVP with 8 cores):
> > > > - start dom0 with dom0_max_vcpus=1
> > > > - remove core 1 from dom0 cpupool: xl cpupool-cpu-remove Pool-0 1
> > > > - create a new pool: xl cpupool-create name=\"NetPool\”
> > > > - add core 1 to the pool: xl cpupool-cpu-add NetPool 1
> > > > - create a guest in NetPool using the following in the guest config:
> > > > pool=“NetPool"
> > > >
> > > > I end with a crash with the following call trace during guest creation:
> > > > (XEN) Xen call trace:
> > > > (XEN)    [<0000000000234cb0>] credit2.c#csched2_alloc_udata+0x58/0xfc
> > > > (PC)
> > > > (XEN)    [<0000000000234c80>] credit2.c#csched2_alloc_udata+0x28/0xfc
> > > > (LR)
> > > > (XEN)    [<0000000000242d38>] sched_move_domain+0x144/0x6c0
> > > > (XEN)    [<000000000022dd18>]
> > > > cpupool.c#cpupool_move_domain_locked+0x38/0x70
> > > > (XEN)    [<000000000022fadc>] cpupool_do_sysctl+0x73c/0x780
> > > > (XEN)    [<000000000022d8e0>] do_sysctl+0x788/0xa58
> > > > (XEN)    [<0000000000273b68>] traps.c#do_trap_hypercall+0x78/0x170
> > > > (XEN)    [<0000000000274f70>] do_trap_guest_sync+0x138/0x618
> > > > (XEN)    [<0000000000260458>] entry.o#guest_sync_slowpath+0xa4/0xd4
> > > >
> > > > After some debugging I found out that unit->vcpu_list is NULL after
> > > > unit->vcpu_list = d->vcpu[unit->unit_id]; with unit_id 0 in
> > > > common/sched/core.c:688
> > > > This makes the call to is_idle_unit(unit) in csched2_alloc_udata
> > > > trigger the crash.
> > > So there is no vcpu 0 in that domain? How is this possible?
> > Easy, depending on the order of hypercalls issued by the toolstack.
> >
> > Between DOMCTL_createdomain and DOMCTL_max_vcpus, the domain exists but
> > the vcpus haven't been allocated.
> Oh yes, indeed.
>
> Bertrand, does the attached patch fix the issue for you?
Oh, just realized that the "Fixes:" tag is referencing the wrong commit,
that should be 70fadc41635b9b62


Juergen

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