Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up at boot time

From: Peter Zijlstra
Date: Mon Jun 17 2019 - 12:04:42 EST

On Mon, Jun 10, 2019 at 05:24:32PM +1000, Nicholas Piggin wrote:
> Nicholas Piggin's on June 1, 2019 9:39 pm:
> > With the change to allow the boot CPU0 to be isolated, it is possible
> > to specify command line options that result in no housekeeping CPU
> > online at boot.
> >
> > An 8 CPU system booted with "nohz_full=0-6 maxcpus=4", for example.
> >
> > It is not easily possible at housekeeping init time to know all the
> > various SMP options that will result in an invalid configuration, so
> > this patch adds a sanity check after SMP init, to ensure that a
> > housekeeping CPU has been onlined.
> >
> > The panic is undesirable, but it's better than the alternative of an
> > obscure non deterministic failure. The panic will reliably happen
> > when advanced parameters are used incorrectly.
> Ping on this one? This should resolve Frederic's remaining objection
> to the series (at least until he solves it more generally).
> As the series has already been merged, should we get this upstream
> before release?

I was hoping for feedback from Frederic, lacking that, I've queued it