Re: SMP lockup at boot on Freescale/NXP T2080 (powerpc 64)

[Christophe Leroy]

Le 07/08/2019 Ã 03:24, Chris Packham a ÃcritÂ:
> On Wed, 2019-08-07 at 11:13 +1000, Michael Ellerman wrote:
> > Chris Packham <Chris.Packham@xxxxxxxxxxxxxxxxxxx> writes:
> > > On Tue, 2019-08-06 at 21:32 +1000, Michael Ellerman wrote:
> > > The difference between a working and non working defconfig is
> > > CONFIG_PREEMPT specifically CONFIG_PREEMPT=y makes my system hang
> > > at
> > > boot.
> > >
> > > Is that now intentionally prohibited on 64-bit powerpc?
> > It's not prohibitied, but it probably should be because no one really
> > tests it properly. I have a handful of IBM machines where I boot a
> > PREEMPT kernel but that's about it.
> >
> > The corenet configs don't have PREEMPT enabled, which suggests it was
> > never really supported on those machines.
> >
> > But maybe someone from NXP can tell me otherwise.
>
> I think our workloads needÂCONFIG_PREEMPT=y because our systems have
> switch ASIC drivers implemented in userland and we need to be able to
> react quickly to network events in order to prevent loops. We have seen
> instances of this not happening simply because some other process is in
> the middle of a syscall.
>
> One thing I am working on here is a setup with a few vendor boards and
> some of our own kit that we can test the upstream kernels on. Hopefully
> that'd make these kinds of reports more timely rather than just
> whenever we decide to move to a new kernel version.


The defconfig also sets CONFIG_DEBUG_PREEMPT. Have you tried without 
CONFIG_DEBUG_PREEMPT ?

Christophe